Kenny Ortega - the choreographer behind the 50 planned London shows the 'King of Pop' was rehearing for when he tragically died in June – revealed the documentary was pieced together from private footage of the star rehearsing and was never intended to be released to the public.

He said: 'The recordings were made so we could use them, then the tapes were destined for Michael's private library. They have a real unguarded honesty to them.

'At first I got so many messages from fans around the world asking to see the shows, asking to see the footage and eventually I realised the journey wasn't over and we had to do this.

'It is for the fans and the film will show the development and intentions of the show, and the concert as it moved closer to London.'

'High School Musical' director Kenny, 59, also claims Michael was getting progressively healthier as he practiced for his mammoth comeback and amazed the performers he had recruited to join him on stage.

He added in an interview with BBC Radio 1: 'He had dancers less than half his age – he was 50 years old and still he would have them falling to their knees in amazement of his moves.'