Timothée Chalamet’s commitment to his role in Marty Supreme led to a behind-the-scenes moment that left his co-star stunned.

In Marty Supreme, Chalamet portrays a professional ping-pong player named Marty Mauser, who won’t back down from any challenge. And that same drive reportedly carried over to the production of the Josh Safdie film. The actor wanted complete authenticity, even when it came to getting spanked by his co-star Kevin O’Leary.

In the movie, Chalamet’s character begs the wealthy power broker Milton Rockwell, played by O’Leary, to fund a high-stakes table tennis rematch in Japan against rival Koto Endo (Koto Kawaguchi) after he originally turned down Rockwell’s offer. Bitter about the initial rejection, the tycoon wants a little payback before helping him. Rockwell’s one condition is that Marty must let him spank him in front of a bunch of people and let him spank him.

In an interview with Business Insider, O’Leary revealed that this was originally supposed to be filmed with a stunt double and a prop paddle. However, Chalamet refused, he wanted to be the one who got spanked instead. The actor said that if the scene was going to be “immortalized,” it had to be his body.

We had a stand-in ass and a fake paddle that supposedly would not put the full force. All of a sudden, Chalamet came on set and said, ‘No, if this ass is going to be immortalized, it’s my a**’.

O’Leary told the publication that he was shocked as he didn’t expect this kind of reaction. The Shark Tank icon even tried to talk him out of it. He said he tried to reason with Chalamet by telling him that it would hurt and could potentially even leave blisters on his body. But the young actor wanted it to be done authentically, and he followed through on his promise.

I said, ‘Look, man, your ass is gonna be blistered, let the stand-in ass do it.’ He said, ‘No.’ I said, ‘I can’t hold back, I’m gonna have to whack your ass.’ He said, ‘I don’t give a shit.’

According to O’Leary, the prop paddle snapped almost immediately, forcing him to use a real one for the remainder of the takes. He estimated that Chalamet endured more than a dozen hits while filming. And, the director allegedly even encouraged him to smack him harder so he could get a better reaction out of the actor.

Josh kept saying, ‘Harder! Harder!’ And the one where you see Chalamet’s face explode, I really whacked his ass. That’s what is in the movie.

Marty Supreme is now playing in theaters.