The "Succession" star appeared as Macaulay's character Kevin's bed-wetting cousin Fuller in the movie, but he tells James Corden on his "The Late Late Show with James Corden" that, despite acting in the film, he was surprised to learn his sibling was the leading man.
"I didn't even know what the movie was about when we were doing it, so it was a fresh, brand new movie when I saw it," Kieran shares. "There's a part in the movie where there's a kid who gets his head counted incorrectly and he goes, 'Bye, bring me back something French!' I thought the movie was about that kid."
"It made sense when I saw it," Kieran insists. "I remember seeing it in the theater at the premiere and I was dying laughing and I was like, 'Oh, that makes sense 'cause Mac was on set all the time.'"
And last week (August 26), Macaulay celebrated his 40th birthday by trolling fans online with a message reading, "Hey guys, wanna feel old? I'm 40. You're welcome..."
"Since I'm 40 I think it's about time to start my midlife crisis. I'm thinking of picking up surfing. Do you all have any suggestions?" he quipped.