Joaquin Phoenix Says It Was 'Impressive' Lady Gaga Lost So Much Weight for Role in New 'Joker' Movie

Joaquin Phoenix praised Lady Gaga ’s striking transformation for their upcoming Joker flick.

At the Venice Film Festival on September 4, Phoenix spoke about how the star slimmed down in order to take on the role as Harley Quinn .

“Stefani also lost a lot of weight,” Phoenix said, using Lady Gaga's first name. “I remember when I first met you in rehearsals and then you went away for like a month and then you came back, you lost a lot of weight.”

He added, “It was really impressive. It seemed very difficult.”

Phoenix hailed this transformation as "impressive," showcasing her commitment to the craft.

“I think we transformed into our characters over a period of time and we continued to hone in every kind of detail,” she said.

Elsewhere in the press conference, Phoenix, who plays the film's titular role, didn't comment too much on what he ate while transforming into the character.

“I’m not going to talk through specifics of the diet, because I just think nobody wants to hear that,” he said.

“It felt a bit more complicated just because there was so much dance rehearsal that we were doing, which I didn’t have last time,” Phoenix explained. “So it felt a bit more difficult, but it is safe.”

Going forward, Phoenix said he likely won't tackle roles that require him to lose weight, as he's almost in his 50s.

“This is probably it for me," he said.

“I know I was responsible last time for talking about it, but it’s difficult to do so that becomes your obsession because you’re working the entire time to get to a certain weight,” Phoenix, lost 52 pounds to play Arthur Fleck in the first Joker film , said.

“So then you end up talking about it, and then it just sounds like an actor going on and on about how much weight they lost,” he continued.

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The Her star added that shedding pounds wasn't good for him.

“By the end of that run I was so sick of myself and angry at myself for making such a big deal about that part , because you just do what you’re f------- supposed to do,” Phoenix shared. “So this time I was like, ‘I’m not going to do that.'”