Bradley Cooper's 'Maestro' a tale of music, marriage and multitasking

Co-writing, directing, producing and starring in his Leonard Bernstein biopic "Maestro" was a terrifying undertaking for Bradley Cooper that turned into a journey of joy and courage.

A passion project years in the making, Maestro is the follow up to Cooper's directorial debut, A Star Is Born.

"In the beginning, realising how much work would be involved, I was terrified. But the more work I put in, and then each day, I became more and more at ease with the idea of being able to ask everybody to go on this journey," he told Reuters at the film's premiere in London on Friday.

"By the end of it, it was just joy and fearlessness."

Bernstein, who died in 1990, was a celebrated US conductor and composer, who wrote classical music and iconic hit musicals like West Side Story.

Maestro focuses on his relationship with his wife, Felicia Montealegre, played by British actor Carey Mulligan.

"Lenny and Felicia were filled with a lot of passion and we were so excited that we were able to put our energy into a story about people that really loved life and lived life in such a dynamic way," said Cooper.

"At the time there was so much mutual love for them as a couple, everyone referred to them as Lenny and Felicia. It feels so appropriate that the film is their story and their love story," added Mulligan, who said being directed by her co-star was her “favourite experience ever”.

"I've never experienced anything like it," she said. "It didn't feel like two separate things. There's no acting required, you just are in the scene, I think that's a testament to a truly great director."

The children of Bernstein and Montealegre were closely involved in the development of the movie. Maestro was made for their family, said Cooper, and everything else, including Oscar talk, is extra.

"We had a really profound relationship with them throughout this whole experience. It really is about serving their parents in this art form and all this other stuff is awesome and it's fun, but it has nothing to do with why we did it."

Maestro starts streaming on Netflix on December 20.