You can't always get everyone back for a sequel, especially if it's one that wasn't originally planned. But sometimes there are murkier reasons why actors don't sign up – or aren't asked back – to continue a film franchise.

"Scheduling conflicts" is the euphemistic term actors and studios often use, but sometimes one or the other party will speak about it once a commercially acceptable amount of time has passed….

1. Rachelle Lefevre in Twilight

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Lefevre played vampire Victoria in Twilight and New Moon but come the third film, Eclipse, Lefevre was dropped and Bryce Dallas Howard picked up the role. According to Lefevre it wasn't her choice – and she wasn't very happy about it.

"I was fully committed to the Twilight saga, and to the portrayal of Victoria," she told Access Hollywood. "I turned down several other film opportunities and, in accordance with my contractual rights, accepted only roles that would involve very short shooting schedules.

"My commitment to Barney's Version is only ten days. Summit picked up my option for Eclipse. Although the production schedule for Eclipse is over three months long, Summit said they had a conflict during those ten days and would not accommodate me.

"Given the length of filming for Eclipse, never did I fathom I would lose the role over a 10-day overlap. I was happy with my contract with Summit and was fully prepared to continue to honour it. Summit chose simply to recast the part."

In response, Summit said it had "acted in good faith that [Lefevre] would be available to fulfil her obligations both in terms of rehearsals and shooting availability for The Twilight Saga: Eclipse," adding: "The fact remains that Ms Lefevre's commitment to the other project... makes her unfortunately unavailable to perform the role of Victoria."

Poor Lefevre – Victoria gets a much juicier part in Eclipse. And poor us for having to tolerate Bryce Dallas Howard's terrible wig.

2. Claudia Wells in Back to the Future

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Wells played Marty McFly's girlfriend Jennifer in Robert Zemeckis's original but when the time came for Part 2, she was replaced by Elisabeth Shue. The decision was Wells' own and came because of an illness in the family.

"My mother had fourth stage lymphoma," she told The Huffington Post. "I had so much happening personally that deep down, I never considered reprising my role and deep in my soul, I knew this was the right choice for me."

An instance where, understandably, an actor and the studio have remained amicable.

3. Terrence Howard in Iron Man

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The first Iron Man was a risky project – a virtually unknown superhero played by a star who wasn't an obvious banker, kick-starting a massive shared universe of the sort we hadn't really seen before.

Turns out it paid off. But not for Terrence Howard, who insists he got screwed over after the first movie's success, claiming producers wanted him to take a massive pay cut for the sequel, believing it would be successful with or without him.

Erm, turns out they were right, and Don Cheadle has held the role of Tony Stark's right-hand man Rhodey ever since.

Howard was not happy and took it out on Robert Downey Jr, claiming he "took the money that was supposed to go to me and pushed me out". Eeps. They made up in 2017, with Howard saying: "We just realised that life is too short."

4. Katie Holmes in Batman Begins

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Even though Christopher Nolan is one of the hottest directors around and Holmes is best known for marrying Tom Cruise and being in Dawson's Creek, it turns out SHE turned HIM down when it came to reprising the role of Rachel Dawes in The Dark Knight.

"Katie wasn't available for the role, which I wasn't very happy about, but these things happen, and I was very, very fortunate that Maggie [Gyllenhaal] was able to take it over," Nolan told Alloy.

It's not entirely clear why Holmes dropped out, with scheduling conflicts cited [insert your made-up conspiracy theory here]. But recently, she told Business Insider that she still stands by the decision.

"You know, I really enjoyed working on the first one and I wish I could have worked with Chris Nolan again," Holmes said. "It was a decision that I made at that time and it was right for me at that moment, so I don't have any regrets. I think that Maggie did a wonderful job. But I really hope that I get to work with Chris some day."

5. Rachel Weisz in The Mummy

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After two Mummys, Rachel Weisz decided not to return to the franchise to play Evie, so she was replaced by Maria Bello. The exact reason why she dropped out is unclear, though.

Some reports suggest that Weisz didn't want to be away from her family shooting in China for five months, others that she didn't want to play the mother of a 21-year-old, and still more that she just didn't like the script.

Whatever reason, she dodged a bullet – The Mummy: Tomb of the Dragon Emperor is one of the worst films we have ever seen.

6. Crispin Glover in Back to the Future

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Glover played Marty's Dad George McFly in the original Back to the Future, but come the second film, Glover was replaced by Jeffrey Weissman.

According to Glover, he refused to do the sequel because the money wasn't right but also for moral reasons – he said he'd fallen out with co-writer and co-producer Bob Gale when he raised objections about the ending of the first film, which implies that the McFly parents are much happier and more in love when they are richer.

Rather than just re-cast, as they did with the part of Jennifer, they made Weissman wear prosthetics for the sequel to make him look like Glover. Glover then sued for use of his likeness without permission and the case was settled out of court.

As of 2015, he still wasn't very happy about it, telling The Guardian: "Me asking the questions that I asked [about the film's ending] infuriated [the film-makers], and they were angry and they wanted to do something that was cruel, which they accomplished."

7. Jodie Foster in The Silence of the Lambs

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After winning a best actress Oscar for The Silence of The Lambs, it was Foster herself who opted not to return for sequel Hannibal – even though her co-star Anthony Hopkins had agreed to come back, and acclaimed director Ridley Scott was on board. Foster was replaced by Julianne Moore.

Rumour has it she didn't like the script, which included Clarice indulging in a bit of cannibalism herself (as she does in the book). Though speaking to Total Film, she was more circumspect.

"The official reason I didn't do Hannibal is I was doing another movie, Flora Plum," she said. "So I get to say, in a nice, dignified way, that I wasn't available when that movie was being shot... I saw Hannibal. I won't comment."

8. Ed Norton in The Incredible Hulk

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Unlike the lack of clarity around the various Bond and Batman reboots, there's no doubt that Edward Norton's The Incredible Hulk is part of the larger MCU (after all, William Hurt reprised his role as Thunderbolt Ross in Captain America: Civil War).

We may never know exactly what happened between Marvel Studios and Norton, who actually helped to rewrite the script, but there's no doubt that there was a big falling out over the 2008 movie. Norton did almost no publicity for The Incredible Hulk, and reports had it that he had fundamentally disagreed with the direction Marvel had taken on the project. When it was announced that Mark Ruffalo would replace him in 2012's Avengers, he wrote on Facebook that "it hasn't turned out as we all hoped".

By 2014 he was taking a more live-and-let-live approach, telling NPR that he "really, really enjoyed" working on the film, but had decided that he "wanted more diversity" in his career rather than getting stuck playing one character (a definite possibility – just ask Robert Downey Jr).

9. Richard Harris in the Harry Potter series

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Neither Albus Dumbledore nor Richard Harris could cheat death forever. The actor sadly died at the age of 72 in 2002 shortly after being diagnosed with Hodgkin lymphoma.

Harris's family reportedly put his friend Peter O'Toole forward as a replacement, but that didn't come to pass. Michael Gambon took over the role from Harry Potter and the Prisoner of Azkaban until the end of the series.

From: Digital Spy