Kieran Culkin Said He Could Hear Nicholas Braun Slapping Matthew Macfadyen in “Succession” Finale 'a Room Away'

Even though the actors were nervously "giggling" before their climactic bathroom standoff, things got serious when it was time to film because, per Braun: "You only get one chance to slap an actor"

It was the slap heard a whole room away.

During the Succession post-Emmys panel moderated by Seth Meyers on Tuesday, Kieran Culkin conceded he wasn’t just on set when Nicholas Braun slapped Matthew Macfadyen during their bathroom fight scene, but that he could hear that slap loud and clear despite being in another room.

“I was there. I was watching in the monitor, which was probably a whole room away and I could hear that slap,” Culkin, 41, said.

Related: Brian Cox Says the Outcome of the Succession Series 4 Finale Was ‘Obvious’

Braun, 35, for his part, joked about why he put so much energy into smacking Macfadyen, 49.

“You only get one chance to slap an actor, and you don't know if there's going to be another take,” he said, before joking, “Luckily there were four, so I kept getting to give it to you.”

Preparing for that scene involved the two actors going over the slap several times the day before and the day of — a ritual they practiced for many of their scenes together, partly to avoid giggling while filming.

“You don't want it to get old, but we don't want to laugh,” Braun added. “We just want to get through it.”

Not laughing during scenes, apparently, was such a challenge for Braun and Macfadyen — who played cousin Greg Hirsch and Tom Wambsgans on the series, respectively — that Succession creator Jesse Armstrong said the crew would schedule two additional hours into the shooting schedule if the stage directions called for the pair to “make eye contact” or indicated “their faces are close.”

“More film. Need more film,” quipped Braun.

Related: Nicholas Braun Shares His Favorite 'Succession' Blooper (Spoiler: It Involves Wrestling with Kieran Culkin)

The actors' onscreen brawl was one of many convincing scenes during the HBO drama’s fourth and final season that helped Macfadyen secure his second Emmy on Monday for outstanding supporting actor in a drama series and a Golden Globe the week before for best performance by a male actor in a supporting role on television.

During his Emmys acceptance speech, Macfadyen thanked his Succession "family," before giving a "special mention" to "my onscreen wife, Sarah Snook, and my other onscreen wife, Nicholas Braun."

"Acting with you has been one of the most wonderful things in my career. Thank you, Nick. Thank you, Sarah. It's been a joy," he added, before concluding, "Thank you to my actual wife, Keeley, my love and my best friend for being here."

Culkin also won a Golden Globe, Critics Choice and Emmy Award for his role as Roman Roy in Succession, taking home each show's awards for outstanding lead actor in a drama series.

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All four seasons of Succession can be streamed on Max.

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