Sir Elton John's biopic will be a "crazy technicolor affair".

The movie is being written by Lee Hall and will follow the superstar singer's journey from birth to rehab. Elton's had a high-profile battle with drug addiction and entered rehab in the '90s, before completely turning his life around.

"I've been working on it with Elton for long time. It's an absolutely huge, crazy technicolor affair," Lee told BBC Radio 4's Front Row.

"[It's] about all the trouble he got into."

The film sees Tom Hardy taking on the lead role in Rocketman, with the actor previously claiming he's used some of Elton's clothes to help him get into character.

Lee is astounded by how open the singer has been with him, explaining he has enjoyed completely "free reign" while working on the script.

"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 this stuff," he said.

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

Lee and Elton have known each other for some time, as they have worked together before. Lee wrote triple Oscar-nominated 2000 movie Billy Elliot and then adapted it for a musical, with Elton providing the accompaniments.

The writer can see many parallels between the 67-year-old singer and the title character of Billy Elliot, a boy who is desperate to make it big in ballet.

"The more I talked to Elton, the more I realised that he was Billy Elliot. He went to the Royal Academy when, I think, he was about 13 and he was studying to be a classical pianist and he discovered Elvis Presley and the rest is history," he explained.

"But I think it's about the struggles that he had, coming from the wrong end of the tracks, with his sexuality. It's what happened next to Billy Elliot, a sequel in a way."

Rocketman will start shooting later this year and at the moment it's unknown whether Tom will show off his vocal talents, or mime along to Elton's back catalogue.