Credit: Warner Bros.

Joaquin Phoenix has been winning raves from critics for his performance in the deeply unsettling new film Joker, and even garnering early Oscar buzz.

But a New York Times story about the film reveals the 44-year-old actor “lost his composure on the set, sometimes to the bafflement of his co-stars.”

“In the middle of the scene, he’ll just walk away and walk out,” Joker co-writer and director Todd Phillips said. “And the poor other actor thinks it’s them and it was never them — it was always him, and he just wasn’t feeling it … If he goes on Jimmy Kimmel and walks off after two minutes, I’d be like, ‘That’s my boy.'”

Phoenix did not, however, ever walk out on his most esteemed costar Robert De Niro, who plays a late-night talk show host in the film. “Joaquin was very intense in what he was doing, as it should be, as he should be,” De Niro said, and called Phoenix a consummate professional.

Phoenix, a three-time Oscar nominee, has said he lost 52 pounds for his role in the dark drama, which reimagines the iconic DC Comics supervillain in a disturbingly plausible and contemporary way.

Joker recently won the top prize at the Venice Film Festival, yet is also generating some controversy. EW’s review of Joker took the unusual step of not grading the film, noting, “entertainment doesn’t exist in a vacuum, and a movie with the message this one hammers home again and again — that life is nasty and short; that no one cares; that you might as well burn it all down — feels too volatile, and frankly too scary, to separate from the very real violence committed by young men like Joaquin Phoenix’s Arthur Fleck in America almost every day.”

Joker is released Oct. 4.

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