The 'All Of Me' hitmaker met the music legends separately but revealed both stars gave him the same advice about taking control of his career.
John exclusively told BANG Showbiz: ''[Prince] is a genius. I've met him a few times. We know a lot of the same people in the business and he was signed to Columbia for a time.
''I met him at some of his gigs earlier on in my career, in 2004 or 2005, and I've been to a few of his famous after-parties, after The Grammys.
''He's one of the best performers in the world. I'm star-struck when I talk to him. I just try not to act too nervous around him.''
The 35-year-old singer had dinner with late 'Bad' hitmaker Michael at a Formula One event in Bahrain in 2006 and talking about ''music and travelling.''
John said: ''Both he and Prince have had their issues with record labels and they gave me advice about publishing rights and how much to give up.
''It's hard to make those changes when you're in the midst of a contract. As you renegotiate you have to renegotiate based on any power you think you have. It's about who has leverage and taking as much control as you feel you can, while also getting as much cash as you think you should get.''
Many ticket-holders couldn't get into the O2 Arena show on Tuesday night (September 19th) because they didn't bring photo ID to match their booking.
An album re-release, a new song and a documentary mark the singer's legacy this year.
The actor plays the titular hero in the forthcoming adaptation.