Following in the footsteps of other rock-and-roll luminaries such as Aerosmith, Sting, Metallica and a guy pretending to be Michael Jackson, Coldplay front-lad Chris Martin will lend his voice and likeness to an episode of "The Simpsons" airing Sunday called "Million Dollar Maybe."
The new episode sees Homer standing up Marge for a date, instead spending his evening winning the Springfield lottery jackpot. He decides to blow some of his newfound cash on gifts for the family, including front-row seats to a Coldplay show for himself and Bart. From their seats, they're able to speak with Martin, and Homer tries to talk his way onstage. Hilarious hijinks no doubt ensue.
and here is the behind the scenes
source : http://coldplay.com/newsdetail.php?id=581