In the summer of 2007 I was asked if I would like to talk to Prince. He was coming to London to play an unprecedented 21-night residency at the 02, and he would grant one journalist an interview during his time in the city. I did not have to consult my diary before taking the assignment. I didn't go to all 21 shows. I went only when summoned, which I think I was seven or eight times. I also went to a number of unscheduled aftershows. On each occasion I waited backstage with Prince's PR, Alan Edwards, or one of his team, for the call to the great man's dressing room. I passed the time talking to members of Prince's band, his dancers, his management team, his associates, the promoters, the security guys. But not to Prince. The concerts were played in the round, so I couldn't watch from the side of the stage. But I was allowed to roam the auditorium and, on two extraordinary nights, to watch from beneath the stage, with the guitar techs, my head at times just inches from Prince's Cuban-heeled boots, or from his hands as he reached down to swap an acoustic for an electric. I'd seen his incomparable live shows before, but this was something else: a rare close-up glimpse of perhaps pop's greatest ever showman — yes, really — at work, his sweat coming at me like sea spray. No, I never got to interview him. He vanished. The story below is an edited version of the piece I wrote at the time about that experience. It has a coda. In the summer of 2009, almost two years after the 02 shows, I was having lunch by a pool in a holiday villa in the south of France with my family and friends, when my phone rang. It was a woman called Maureen from Los Angeles. Prince, she announced, was ready for his interview. What? Prince, she repeated — yes, the pop star — was ready for me to interview him. Now. Where was he, I wanted to know? In Minneapolis. I told her I was in the south of France. She seemed unimpressed. I said I would fly to Minneapolis as soon as I could but I would have to go back to London first. Could he wait a day or two? She said she would call me back the following day. I waited by the phone, by the pool. Nothing. I called and left her a message. Should I book a flight to Minneapolis? Still nothing. I never heard from her again. I'd missed my slot. Prince don't wait. I'm not sorry, really. Like anyone who got to see him play, it was enough to be in the room while a genius did his truly spectacular, life-affirming thing. Like the man said, "So many hits, so little time" — but he made it all count.

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Friday August 24, 2007. The 02 Arena, London. Showtime approaches on night ten of Prince's 21-date residency. I'm pressed against a girder in a cavernous, echoing backstage area, trying to keep out of the way of a team of roadies in high-waisted jeans, faded promo T-shirts and dusty work boots, paunches overhanging their utility belts, hairstyles unchanged since Deep Purple's Stormbringer tour of 1974.

Pity the journalist in this situation who trips over a crucial wire, needlessly interrupts a walkie-talkie conversation to ask directions to catering, or gets in the way of a two-man team heaving a box of equipment towards the stage. I've done all three, and the show hasn't started yet. My orange access-almost-all-areas sticker has got me this far but I'm still regarded with suspicion by the crew.

Stone-faced security guards in hi-viz tabards ask me what I'm doing here and look incredulous when I tell them I'm a journalist hoping to interview Prince. Seen-it-all promotion executives in capacious grey suits stare menacingly at their Blackberrys, seeking confirmation of this strange news. Prince's PR has to intercede more than once to make sure I'm not thrown out. No one smiles.

At 8.20pm, the band appears. The New Power Generation are a flamboyant bunch. The backing singers are a flock of eccentrically plumed birds of paradise. The horn section is made up of zoot-suited jazzers. Then there are the Twinz, two improbably supple Australian sisters whose relationship to their recently divorced boss has been the source of much conjecture since their arrival in the UK a few weeks previously.

Psyching themselves up for the show to come, the musicians whoop and hug and jog on the spot. All of this is part of an elaborate waiting ritual. They're waiting. The roadies are waiting. The security guys are waiting. The promotions executives are waiting. The PRs are waiting. We're all waiting. And we've been waiting some time. Personally, I've been waiting for three days and nights. Nights that have lurched into mornings and crept in to bed as the sun comes up. I've seen Prince play twice already over the past two weeks, delivering concerts extraordinary in their intensity and virtuosity – greatest hits packages that reinvent some of the most famous pop songs of the last twenty-five years: "1999"; "Purple Rain"; "When Doves Cry" "Little Red Corvette"; "Raspberry Beret"; "Kiss"; "If I Was Your Girlfriend"; "Nothing Compares 2 U"; "Diamonds and Pearls".

But I'm yet to actually meet Prince. On one occasion I witnessed him helping himself to crudités in the backstage refectory, but as I made to approach him, a panicked operative held me back. "Not now," she hissed. Another time, in the early hours at a private members club in East London, I saw him at close quarters again, when he made an unexpected appearance at the party following the premiere of The Bourne Supremacy. Again, I was prevented from talking to him, this time by a velvet rope and the attentions of his bodyguards. I'm not sure even the film's star, Matt Damon, made Prince's acquaintance.

Tonight, I'm told, could be the night. Prince apparently knows I'm here. He has personally sanctioned my presence. Indeed, he has requested it. On each of the occasions I've spent time backstage and in the audience at his shows, as well as shaking a slightly weary leg at his famous early-hours, after-show jams in the complex's nightclub, Indigo, I've passed the preceding afternoons checking my mobile, waiting for a call from Alan Edwards, his British PR. On a couple of occasions I've been stood down. But this is the third time I've been told to come to the venue immediately, where Prince and his entourage will be expecting me.

I've got sheets of questions prepared, questions that will sweep away the shroud of mystery surrounding the enigma, revealing the real man within. I'm carrying notebooks on which I will jot impressions of searing insight that will reveal essential truths about the methodology of one of popular culture's most mysterious figures. My Dictaphone is on hand to record the surprisingly bawdy bon mots of this legendarily sober individual. I have many back-up tapes and multiple spare batteries, should the notoriously private entertainer be unexpectedly moved by a spirit of personal revelation. If my journalistic career doesn't work out, I could open an on-site Rymans next door to the 02 branch of Nando's, for those who fancy some stationery to go with their Peri-Peri chicken.

Meanwhile, we wait, everyone staring at the same object. Weirdly, it's a packing crate on wheels, the kind that is used for transporting heavy equipment around the world. It's about half the size of an old Fiat 500, or twice the size of a coffin. There are many of these crates stacked up in our vicinity, but this one is slightly different. It has been modified. Earlier, temporarily separated from my minders, I had a chance to inspect it. From the outside it looks perfectly normal, black with metallic rivets. Inside, however, it is tricked out from bottom to top in purple velvet lining. And there's a tiny, bucket-sized cube at the far end from the door. That's also upholstered in purple velvet. It looks a bit like a stool. Wait, it is a stool. There's a peep-hole slashed into the door, at precisely the eyeline of a sitting Prince. Curious.

Then the word goes round: "He's coming". And so he is. He appears from a billowing, white curtained corridor leading Prince knows where. He's wearing a white frock coat, white hat, white trousers, white boots.

He is, of course, tiny; even famously small famous people are smaller in real life. At this short distance – ten paces perhaps – one can marvel at the extraordinary fluidity and economy of his movements. He's there, and then he's sitting inside the purple-lined packing crate, and then they're closing the door, and then he's gone. Then they're wheeling him outside into the auditorium. If you didn't know – and if you're outside in the auditorium, how would you know? – you'd think this was just another packing crate being wheeled under the stage.

Moments later, as if by magic, invisibly decanted from his crate, Prince appears centre stage and the band launches into the first number, "Musicology Jam". Licensed to roam, I take a VIP seat at the lip of the stage. After ten minutes or so, I'm beckoned forward and inside the Love Symbol-shaped stage, where I crouch with the guitar techs. As Prince struts and gyrates, tearing through "Play That Funky Music", "Cream" and "U Got the Look", his dancing boots are only six feet from my head.

I once got this close to a tiger, on a safari in Rajasthan, India. The experience is somehow analogous. I felt the supreme, primal presence of a beast that was rare and magnetic, a thing of stupendous elegance, regal bearing and almost mystical power. Time seemed to stop. I held my breath for far longer than advisable. On some instinctive level, I recognised that despite its physical proximity it would remain profoundly unknowable.

I never got to interview the tiger, either.

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Summer 2007 will be remembered for many things. It was the summer of Madeline McCann; of flash floods; foiled terror attacks; the last days of Tony Blair's premiership and the first of Gordon Brown's. For those who live in London, especially those lucky enough to get a ticket for the 02, it will also be remembered as the summer of Prince.

Beginning on August 1st and continuing until September 21st, he played 21 completely sold-out nights at the 02. At 16,500 people per night, that's almost 350,000 funk-seekers entertained, including phalanxes of London movers and shakers and a cavalcade of international stars: P Diddy, Alicia Keys, Penelope Cruz, Elton John, Amy Winehouse and Naomi Campbell among them.

The man who organised all this was Rob Hallett, a veteran British rock promoter who now glories in the title President, International Touring, AEG Live.

Hallett, a straight-talking north Londoner, has toured with some of the biggest names in pop. In the past twelve months alone he has orchestrated concerts for Bon Jovi, Justin Timberlake and Leonard Cohen, but he says he's never collaborated with anyone quite like Prince. "Prince is a genius," he says. "He's very special. He's not like you and me. He's got a vision. He's not crazy. He's intelligent, witty, charming. He's focussed, self-motivated. He just gets it. He's a dude."

Prince first suggested the idea for a series of 21 concerts in London over drinks at Boujis, the Sloaney South Kensington nightclub. Hallett says he tried to persuade Prince that expecting to sell out 21 nights was too ambitious, even for him.

"It was a big gamble," Hallett tells me. "It's a multi-million pound commitment. People thought I was off my tree: 'Oh, God, Hallett's lost it again.'"

But Prince would not be persuaded. Tickets for the first 15 nights went on sale on May 10th, and were gone in under an hour. Two weeks later, when tickets for the remaining six nights went on sale, they also sold out. The gross receipts were more than £10 million. Subtract VAT and PRS – royalties paid to composers and publishers when music is performed live – and the box office is still what Hallett calls "big numbers". "And there's merchandise on top of that," he says. "And we did very well with the merch.

"I think it's the longest residency ever," says Hallett. "I don't think there's anyone else who could do it. All due respect to the Stones, but they tour every two years, which is fantastic for the fans but it doesn't leave that level of demand. It's not as hot a ticket. Same thing with Madonna. Because Prince plays here so seldom, and he's such a legendary character, people had to be there. It's a feat I don't think anyone will achieve again."

Other factors increased the demand. It was announced that Prince was "retiring his hits": he might never play "Purple Rain" and the rest again. Fans knew that he would play bonus after-show gigs. It was promised that each night would be different, and therefore unique. (The band rehearsed 130 songs for the 21 Nights, and were only handed set lists shortly before each show. One evening I was there they were frantically working out a horn arrangement for INXS's 1985 hit "What You Need" – or "What U Need", since this was the Prince version – which had been sprung on them at the eleventh hour.)

Tickets were priced at a more than competitive £31.21, 3121 being the name of a Prince album from 2006, and the street number of a house Los Angeles where Prince once lived, and partied; it has come to represent, for him, a mythical space of music and dancing. "I wish he'd moved to 9494," Rob Hallett says. "It would have been much more lucrative. Then again, thank God he didn't move to 1518."

Another marketing masterstroke was Prince's decision to give away a CD of his new album, Planet Earth, with each copy of the Mail on Sunday sold on Sunday June 28th, producing a huge spike in circulation, enraging Sony, Prince's record company, and making news around the world.

"At the time I questioned that, like most people in the music industry," says Hallett. "You give away your old music maybe, but you sell your new music. Prince was like, 'You don't get it. We cut out the middle man.' Now of course everyone and their great aunt Fanny's giving away their music. Truly remarkable."

Hallett spent as much time with Prince while he was in London as anyone, and has seen him in the States on half a dozen occasions since. They have shared many nights on the town, here and elsewhere. He must know the man pretty well. "Can you ever really know Prince well?" he wonders, when I ask him.

This is a question I hear repeated often by those around him. Alan Edwards, who has worked for Prince many times, reacts similarly. Even Randee St Nicholas, the photographer who has collaborated with Prince on "21 Nights" (Atria, £30), a new book from which the photos on these pages are taken, writes in her introduction that, "to know [Prince] is to know that you probably will never really know him and to question that is a waste of time."

Backstage at the 02 I have nothing to waste but time, so I spend a good deal of it asking members of the New Power Generation what the real Prince is like.

"He's a beautiful human being," says Shelby J, a warm and boisterous singer from North Carolina "He's caring and generous and he doesn't hesitate to impart his wisdom. He's one of the most amazing musicians who ever lived but he's also one of the cats. Working with him is the biggest thing that's ever happened to me in my life. He's the general and we're the true funk soldiers."

When I push for more concrete details, she offers a gnomic but definitive summary: "He's the boss, apple sauce."

"He's like a conductor," says Greg Boyer, the NPG trombonist. "You keep one eye on him at all times and take your lead from him. It's like a language, a physical and musical language. You have to keep up." I'm not the only Prince-watcher to invoke the image of a big cat when discussing Prince. "Ever watch a cheetah taking down a gazelle?" asks Boyer. "The other cheetahs better be right there, or they don't eat!"

Spending time with Prince, according to Renato Neto, who plays keyboards, is "as normal as hanging with one of my homeboys. He works hard. But he can also be class clown. The perception from the outside and how things really are, it's like night and day. He has a blue-collar mindset: wake up, put on the hard hat, go to work."

This sounds unlikely to me. But the workmanlike ethos Neto describes is reflected in the atmosphere backstage. One might be excused, given the man's reputation, for imagining that the backstage scene at a Prince concert would be a recklessly orgiastic tableau vivant of writhing bodies, but as far as I can see it's nothing of the sort. Most of the time, you could hear a plectrum drop. People go about their business with quiet, determined efficiency. Professionalism, rather than hedonism, is the order of the evening.

Only the presence of the bodacious Twinz, real names Nandy and Maya McLean, hints at more illicit offstage delights. But when I try them for some prurient gossip as they pick at their pre-show salads, they're as tight-lipped as anyone.

The Twinz would have me believe that Prince is like any other person: a man who loves to go out in the evening, but is equally happy spending a night in watching DVDs. "He's a boss and a friend at the same time," says Nandy.

Maceo Parker, famously James Brown's long-serving saxophonist, won't even discuss his current employer. When, following much negotiation, I'm hustled into his dressing room at about 1am, the great man responds to my first question with some displeasure. "Maceo don't talk about other people," says Maceo. "I talk about Maceo Parker."

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Prince's residency at the 02, says Rob Hallett, "will define that building for many years to come." It will define Prince, too, as someone other – someone better - than the bonkers Eighties has-been as which he's often been portrayed.

It's true that his reign as the world's greatest songwriter – a reign that lasted from 1980 (Dirty Mind) to around 1988 (Lovesexy) – has long been over. Something went awry in the Nineties, and it's certainly the case that he has occasionally seemed more than a little loopy: ditching his name and replacing it with a symbol; scrawling Slave across his face in eyeliner to express his anger at record companies; becoming a Jehovah's Witness. But his preeminence among live pop performers must surely be unchallenged.

On stage, he is an explosive composite of Elvis, Jimi Hendrix and James Brown, to name just a few. His music takes in gospel, soul, rock, funk, hip-hop, disco, electro, jazz, blues, R&B and just about every other popular genre of the past sixty years. Lubricious, libidinous, shamanic, athletic, filthy and even funny, he's a 50-year-old Minneapolitan black man playing a white guitar over a mixed-race bass-line, an androgynous swordsman, effete but never effeminate, and he remains the most enduringly fascinating of the great triumvirate of Eighties American pop stars made up by himself, Madonna and Michael Jackson.

Rob Hallett remembers many highlights from the 02 shows, but one in particular stands out: "It must have been half past three in the morning in Indigo and Amy Winehouse comes on. That was a remarkable moment, seeing this frail, demure little figure singing "Love is a Losing Game", with this wild man spinning around her doing guitar licks from hell. I can still close my eyes and picture it. It was unreal."

I'm sorry to have missed that, but I did gather my own fair share of indelible memories. The one I can't shake was a delicate piano medley that ended in the tender, lovely "Sometimes It Snows in April", from his 1986 album Parade. I was no more than fifteen feet from where Prince was playing and singing, and for a brief moment we were the only two people in the room.

Of course, the opportunity to be the only other person in a room with Prince was exactly what I'd been hoping for all along. It's why I was there. It didn't happen. Sometimes, I reasoned, perhaps it really is better never to meet your heroes. That's what I told myself at 4.30 that morning, anyway, as I wandered about the 02 looking for a purple velvet-carpeted packing case in which to nod off.