After 27 years of rumours and urban legends around Michael Jackson's guest appearance on The Simpsons, Matt Groening has finally straightened everything out: they "really did have him" playing a mentally ill man who believes he's Michael Jackson.

It really is Jackson voicing Leon Kompowsky in the 1991 episode 'Stark Raving Dad', but it's not him you hear singing the 'Happy Birthday Lisa' song. Fans had argued for years over whether Jackson had actually taken part, especially as he was credited as John Jay Smith for the episode to keep his profile down.

Groening told The Weekly that he initially put the phone straight down when Jackson called and announced himself, as he had "a voice that sounds like somebody doing a Michael Jackson bit". Jackson rang back, though, and convinced Groening to have him on the show as he "loved Bart".

The confusion sprang from the fact that Jackson was restricted from singing on the show by his record contract, so impersonator Kipp Lennon took over.

“[Jackson] didn’t want credit for [it], or there was some kind of deal with his record company or whatever, so when it came time to sing the songs, he had a sound-a-like singer. He stood there and watched the guy, who was so nervous, who had to sound like Michael Jackson, and then he giggled,” Groening recalled.

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The character of Kompowsky was meant to return in a later episode under the impression that he was Prince, with His Purpleness providing the voice. However, Prince didn't like the script and said no.