Joaquin Phoenix reacts to clip of his expletive-laden outburst on Joker set

But it's now being suggested that the clip was fake

Joaquin Phoenix was confronted to a clip of himself having an expletive-laden outburst on the set of Joker and told Jimmy Kimmel he found the footage “embarrassing” - though all may not be what it seems.

The actor, who plays the titular Batman villain in a film coming out this Friday, 4 October, discussed his work on the set of Jimmy Kimmel Live on Tuesday night.

Kimmel told Phoenix that director Todd Phillips had sent him an outtake reel, which he said included footage of Phoenix venting at director of photography Lawrence Sher, whom he calls Larry.

In the video, Phoenix complains about “constant whispering” on the set, adding: “Just shut the f*** up” and “I’m trying to find something real.”

But his representatives have since insisted that the clip was a "joke outtake".

More profanity follows in the footage until Phoenix comments on someone apparently comparing someone else to the singer Cher. “It’s not even an insult,” Phoenix says. “Cher, really? She’s a singer, actor, dancer, fashion icon. How is that a [profanity] insult?”

Phoenix eventually declares “I can’t do this” as he gets up and leaves – something he also did regularly during takes if he wasn’t “feeling it”, according to Phillips.

After the clip play during Kimmel’s show, Phoenix told the host: “This is so embarrassing.”

“Sometimes movies get intense because there are a lot of people in a small space and you’re trying to find something so it can feel intense,” he added. “But... that was supposed to be private. I’m a little embarrassed. I’m sorry about that.”

Turning to the audience, he added: “I’m sorry you guys had to see that.”

Phoenix said none of it was Sher’s fault and eventually asked Kimmel: “Can we move on?” – before commenting on the moment some more.

“I should probably publicly apologise to Larry,” he added. “Larry – the thing is though, I am sorry but he did whisper constantly while we were trying to work and sometimes it’s really hard to find the emotion that you’re after.

“So it was wrong of me, I’m sorry, but he shouldn’t have done it.”

While Phoenix’s reaction seemed genuine, this might be more of a testament to Phoenix’s acting talents than a mark of authenticity, since his representative has since told EW that the clip was a “joke outtake”.

After watching Kimmel’s show, many social media users appeared convinced that the footage was real, while some suspected it might have been a joke but couldn’t tell for certain.

Phoenix, of course, is no stranger to performance art, which he practiced extensively in the 2010 mockumentary I’m Still Here co-produced by Casey Affleck.

Phoenix recently revealed he didn’t converse with his co-star Robert De Niro on the set of Joker despite being a fan of the actor.

Joker has caused controversy over fears that it could inspire real-life violence due to its portrayal of the DC Comics villain.

In New York City, undercover police officers will reportedly be deployed during screenings.