"I think in a lot of ways he would have been like David Bowie, very moved by the internet"
Michael purchased the piano at auction 20 years ago
A mix of old footage and new content will air later this week
The Beatle spoke to Lennon's son Sean for 'John Lennon At 80'
'Grow Old With Me' was released a month before Lennon's death in December 1980
Lennon played live with Elton in 1974 after losing a bet with him
"It really, really would have been a heartache to me if we hadn't have reunited"
"There were a few that were clearly by young songwriters who don't quite know how to do it"
The auction marks 50 years since the legendary band broke up
The new documentary will mark Lennon's 80th birthday.