It was obvious from the Peacock's first performance that he was a natural performer, and clearly had experience singing onstage. His other big clues are: he chose to be the Peacock because he has a "love of the spotlight," has been performing since he was five years old, can play piano, and has performing "in [his] DNA."
He also tells the panelists he was "dear" friends with Michael Jackson, and says, "It's probably been a while since your mom had a poster of me on her bedroom wall." Former teen idol, eh?
So, who could it be? Donny Osmond had a longtime friendship with Jackson, the King of Pop, and has been performing since he was a kid. Osmond would also make the poster comment check out, as well as having performing in his DNA (he was a part of his family's band, The Osmonds). As a talk and game show host, record producer, and author, you could also say he clearly loves the spotlight.