At the London Film Festival premiere of Tony Gilroy’s “Behemoth!” on Tuesday, Pedro Pascal said learning to play the cello convincingly for the film was the most challenging thing he’s done in his career.

Pedro Pascal said, “I would choose fighting The Mountain in ‘Game of Thrones’ over learning how to play the cello convincingly.”

Pascal plays a gifted cellist who returns to Los Angeles after nearly two decades of touring. The role, he said, scared him more than anything else he’s taken on.

“I’d never been so afraid,” he said. “I’ve been nervous about other jobs and the physical…emotional demands, but it was nothing like this.”

He’d rather revisit one of his bloodiest on-screen moments than do it again. “I would rather be, I don’t know, tossed off of a cliff with Nicolas Cage than have to learn how to play the cello,” he said.

The fear didn’t last once he actually picked up the instrument, which he’s long called his favorite. “Once I held the cello, I felt good,” he said.

Beyond the family drama, “Behemoth!” turns its attention to the world of film scoring, a part of moviemaking Gilroy said even seasoned crew members had never seen up close before filming. Actor Eva Victor said musicians working on the production kept telling the cast and crew, “Finally, a movie about us.”

Alexa Swinton, the 17-year-old “Thunderbolts*” star who appears alongside Pascal, said working with him showed her that success and kindness can go together, pointing to his grace and politeness on set.