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

Hardy is all geared up to portray the 67-year-old musician in the biopic, which will focus on the musician's struggle with addiction, reports contactmusic.com.

"Billy Elliot" writer Lee Hall is the scriptwriter for the project and said that Elton personally handed him his private journals.

He said: "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 his lowest ebb when he decided to seek for help.

He 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."