Bradley Cooper said transforming into the legendary composer Leonard Bernstein for his new film “Maestro”, released on Netflix on December 20, forced him to grow up. The 48-year-old actor spent years researching, writing, directing and starring in the film about the most famous American conductor and composer of the 20th century.

The film focuses on the deep and complex relationship between Bernstein and his wife Felicia, played by Carey Mulligan -- one of real love burdened by his many dalliances with young men. AFP sat down with the two stars backstage at the Theatre de Chatelet in Paris, where they had stopped by to meet the cast of “West Side Story”, Bernstein’s most famous composition.

Q: Bradley, you spent months learning to conduct for the role. Could you jump in and lead the orchestra here?

Cooper: Absolutely not! It would be a calamity (laughs). I learned to conduct six minutes of Mahler. If we did that, I could get away with it -- maybe!

Q: What did you learn about conducting?

Cooper: It’s like riding a stallion. You’re leading the orchestra but you’re also recognising that they’re a breathing organism that’s very powerful and has its own mind. Lenny’s genius was that he could be hard but he always did it with love. And he knew what he was doing. He married romanticism and passion with real musical acumen.

Q: Carey, was Felicia a victim in this marriage?

Mulligan: She was determined in her own mind not to be. Of course she sacrificed a lot, but she did it wholeheartedly, without question, and it was only later in her life that it caught up with her.

Q: How would she feel about being portrayed on screen?

Cooper: The children said Felicia would be horrified because she was such a private person, but secretly joyous that Carey Mulligan was playing her (both laugh). Mulligan: I wrote her a letter when we were about to start filming. Obviously I didn’t send it anywhere. But I wrote ‘I hope this is alright, don’t be cross with me.’ (laughs) I played Nina in “The Seagull” (Chekhov’s play) when I was 21 and it changed my life. I spent the next 15 years trying to find something that felt like that, and I found it in Felicia.

Q: How has the experience of becoming Bernstein changed you?

Cooper: I became an adult through this film, by incorporating the traits Lenny lived his life by, which is an unrelenting pursuit of what one wants to do. I’ve always been apologetic about it before, at least to myself, and I wasn’t on this movie, partly because I had an incredible partner in Carey, who allowed me to be bold.

Q: What drew you to the story -- the music or the relationship?

Cooper: The first thing was being obsessed with conducting. I thought I could pull off playing a conductor because I was so in tune with it since I was a kid.

But in researching and writing, the intriguing thing was this relationship between Lenny and Felicia, and that became the north star. The conducting became just a story point.

Q: What would you like to ask Lenny?

Cooper (long pause): I would ask him if he feels lost. In those last years after she died -- did he feel free to live his best life? Does he wish he could have spoken to somebody to find a sense of peace?

Q: You’ve made a film about rock music (“A Star is Born”) and now classical. What’s next?

Mulligan (interrupting): Techno! — AFP