How on Earth did Mick Jagger end up rapping a verse on ‘T.H.E. (Hardest Ever),’ the first single off Black Eyed Peas singer’s new solo album, '#willpower.' Turns out, first dropped the name Jagger only because he actually didn’t want anybody to guest on the track -- and thought the collaboration would never happen. says that when he finished the song, he "went to play material for the label and [Interscope chairman] Jimmy Iovine’s like, 'Yo, this is dope. Who are you gonna put on it?'," he tells "I’m like, 'What are you talking about? It’s finished, it’s me.' So, he’s like, 'Oh, you don’t [want to] feature no one?'"

"You play your music and the first thing someone says, 'Who’s gonna be on it?' So I think of the hardest [collaborator to get] ever," Will continues. "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."

Not only did Will end up landing Jagger for 'T.H.E. (The Hardest Ever),' but Iovine -- formerly a big time producer who has worked with everyone from U2 to Stevie Nicks to Tom Petty -- came out of production retirement to work on the track, the first time he's done so in decades. "Jimmy’s like, 'Mick Jagger and the Rolling Stones are like my Tribe Called Quest, my De La Soul, my N.W.A. I wanted to be like Mick when I was young,'" Will explains.

"He produced Mick’s vocals, and this was the proudest moment of my life," Will 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."

Unfortunately, 'T.H.E. (The Hardest Ever)' isn't the "dopest ever" track for most of us Stones fans. The song may be perfectly tailored to the millions of Black Eyed Peas lovers out there, but many classic rock listeners were left scratching their heads when the tune hit the Internet this week. Jagger tries his hand at rap-singing, and the results leave much to be desired.

Don't believe us? Take a listen here and then tell us what you think.