It's been a good year for Mick Jagger. He's  the subject of the #1 hit "Moves Like Jagger," but he's also featured on's brand new single "T.H.E. (The Hardest Ever)," which the Black Eyed Peas frontman debuted on the American Music Awards Sunday night.   But as Will tells, it wasn't his idea originally to get Jagger on the track --  the idea only came to him after he played an earlier version of the tune for Interscope Records chairman Jimmy Iovine.

Will tells Rolling Stone, "I went to play material for the label and Jimmy Iovine's like, 'Yo, this is dope.  Who are you gonna put on it?'  I'm like, 'What are you talking about? It's finished, it's me.' So, he's like, 'Oh, you don't feature no one?'"  So I [thought] of the hardest thing ever.  And it happened -- Mick Jagger.  I just wanted to throw something out there that I thought could never be possible so they would stop asking me."

To Will's surprise, not only did Jagger agree to appear on the track, but in doing so, he helped Iovine fulfill a long-time dream.  A former top record producer, Iovine had worked with stars like U2 and Stevie Nicks, but he'd never worked with Jagger -- one of his all-time idols.  When Jagger said yes, Iovine got to produce Mick's vocals on the track, and Will takes credit for bringing them together.  "This was the proudest moment of my life," he says.  "Winning a Grammy is cool, but the guy who helped you out -- and then you got to see him execute one of his dreams -- that's just the dopest ever."

"T.H.E. (The Hardest Ever)" is now available on iTunes.  It's the lead single from Will's upcoming solo album, #willpower.