Bradley Cooper spent over six hours in makeup for his role as Leonard Bernstein in 'Maestro'.

Carey Mulligan and Bradley Cooper in Maestro

Carey Mulligan and Bradley Cooper in Maestro

The biographical movie tells the life story of acclaimed American composer Bernstein, the man behind the musical classic 'West Side Story' (1961) from his younger years, all the way until his final curtain call.

Cooper, 48, plays Bernstein, while Carey Mulligan portrays the conductor's wife, Chilean actress Felicia Montealegre.

During an interview with at the BFI London Film Festival, Makeup Department Head Sian Grigg revealed that Bradley's makeup to play the older Bertstein took an excruciatingly long time and it was not an easy day's filming for Cooper, 48, because he was also directing the project as well.

Grigg said: "The aging took the longest. When Carey was older, that was when she was in her 70s and she was dying of cancer, that was the hardest and longest make up ... We started in [her] early 20s, so it was a long journey for her, and many decades of different makeups and hair.

"But nowhere near as long as Bradley's makeup, because his was really impressive and really long.

"I just don’t know how he did it. He did six hours in the morning, and did a whole day of directing it was phenomenal. I just take my hat off to him, I don't know how he managed to do that, but he did a great job."

As well as putting himself through the lengthy prosthetic process, Bradley made sure he fully immersed himself in the life of the composer by speaking with his daughters, Jaime Bernstein and Nina Bernstein.

Grigg said: "They were quite involved, especially with Bradley.

"I know they had many conversations with him and they were thrilled the film was being made. Their parents were such amazing great people. It was just a privilege to learn about the family really."

'Maestro' will arrive in cinemas on November 22 and Netflix on December 20.