Sir Elton John has revealed the secrets of his rehab diaries for his upcoming biopic starring Tom Hardy.

The 'Dark Knight Rises' star is to portray the 67-year-old musician in a new film, which will focus on his struggle with addiction, following his decision to reveal the secrets of the diaries he wrote while in rehab.

'Billy Elliot' writer Lee Hall - who has written the script for the project - claims Elton personally handed him his private journals.

Hall told The Sun newspaper: ''One day he took me to his house and opened a safe and he had all his private diaries that nobody had seen from when he was in rehab and left me there to read all his stuff.

''But he's never commented once on the script, he hasn't interfered at all.''

Elton entered rehab in the 1990s, at which point he was heavily dependent on drink and drugs, and he's confessed in the past that it was only when he was at his lowest ebb that he decided to seek help.

Reflecting on his troubles, Elton explained previously: ''I would have an epileptic seizure and turn blue and people would find me on the floor and put me to bed and then 40 minutes later I'd be snorting another line.''

Hardy, 36 is currently shooting in London for the Kray twins biopic 'Legend' and has a number of films lined up for release including 'The Drop', 'Child 44' and 'Mad Max: Fury Road'.