The Beatles legend Sir Paul McCartney, 77, famously made a guest appearance in an episode of The Simpsons. The Hey Jude singer and his late wife Linda McCartney did a voiceover in an episode, which saw Lisa stop eating meat.

But Paul's appearance on the popular animated show came with a stipulation that The Simpsons producers had to follow, according to the show's consultant David Mirkin.

Speaking in a candid interview in this week's Radio Times magazine, he revealed the show staff had to make a specific "promise" to the legendary star which they still follow today.

David explained that Paul wanted main character Lisa Simpson to remain a vegetarian on the Channel 4 programme.

He remarked: “When I asked him to do the vegetarian episode, he agreed but made me promise to keep Lisa as a vegetarian — and I was happy to comply, because I’m a vegetarian, too.

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