Ang Lee will direct a Bruce Lee biopic. He cast his son, Mason Lee, to play the iconic martial artist. In a new interview, one of the film's producers, Lawrence Grey, revealed how Mason turned into a “stone-cold killer” for the biopic.

Production on the Bruce Lee biopic has been a long road, something Grey acknowledged. This played to their advantage, though.

“The advantage that we also had to Mason [was], as you pointed out, this project's been being developed closely for many years, and we were able, for five years, to train Mason and turn him from the early days where he's a very fine actor, but clearly the son of a very successful Hollywood director, to a stone-cold killer,” Grey told Collider.

This meant that Mason Lee had to learn Bruce Lee's iconic fighting style — which was unique to him. “I mean, anyone who can fight like Bruce Lee is a maniac, is a killer,” Grey said. “And through that process of training, through reading all of Bruce's material, training in the various martial arts he trained in, we were really able to hone that in.”

Most recently, Bruce Lee was played by Mike Moh in Quentin Tarantino's Once Upon a Time in Hollywood. In the film, he faces off with Cliff Booth (Brad Pitt).

If there was anyone fit to make a Bruce Lee biopic, it'd be Ang Lee. Known for his martial arts films such as Crouching Tiger Hidden Dragon, the versatile director has also helmed superhero films (Hulk) and romantic dramas (Brokeback Mountain). Other film credits include Life of Pie and Gemini Man. Mason Lee is the only confirmed cast member of the biopic and is known for his role inThe Hangover Part II. Production on the Bruce Lee biopic will begin soon after the SAG-AFTRA and WGA strikes, Collider noted.