He said: ''It's been a heartbreak. Obviously I knew Michael. I knew Whitney too and I understand Amy came to my concert in England a couple of years ago.
''I was thinking about us doing a duet - an old Marvin and Mary Wells song called 'Once Upon A Time'. It would have been amazing.''
The 63-year-old singer also doesn't enjoy having his music categorized because he thinks labels are ''bulls**t''.
He said: ''I've never said I was a soul artist or an R&B artist. They're just labels.
''When you're soul it means black and when you're pop it means white. That's bulls**t. If it's good, it's good.
''It's like that old Jerry Reed song, 'When you're hot, you're hot, when you're not, you're not.' ''