Cillian Murphy has revealed the reasons he believes his Oppenheimer costar Matt Damon dubbed him the “worst dinner companion imaginable.”

The Irish actor, 49, chalked it up to him trying to remain in character as the father of the atomic bomb while the pair were making the movie, even when cameras weren’t rolling.

60 MinutesScott Pelley told Cillian in a segment that aired on Sunday, February 18, about Matt’s dinner companion diss, adding, “What he meant by that was when you’re working on a film — when you’re being the character — there’s very little room in your head for anything else.”

“I’ve always been like that, I think,” Cillian replied. “It’s because, to me, you have the time on set, which is a short enough time. You have 10 hours, maybe. And then the other part, if you’ve got a significant part, you’re having to keep your lines fresh.”

Cillian added another relatable reason why he didn’t like staying up and going out to dinner. “And then the other big thing for me is sleeping. I love sleeping and I need sleep.”

“At the time, yeah, you just don’t have the room … in your head and you want as much sleep as possible,” he continued, adding that since filming wrapped, he’s had much more enjoyable nights out with Matt, 53.

“I’ve had lots of lovely dinners with Matt Damon since the movie has finished, and we’ve been out promoting it and stuff,” he shared.

Actress Emily Blunt, who played Cillian’s wife Katherine “Kitty” Oppenheimer in the Oscar-nominated film, explained in July 2023 how he wouldn’t join the rest of the cast for a meal when they would get together after a day of filming.

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“We were all in the same hotel in the middle of the New Mexican desert. We only had each other. Me and Matt were roommates and we were like, ‘Let’s go to have dinner,'” she recalled to People, although Cillian rarely joined them. “The sheer volume of what he had to take on and shoulder is so monumental,” Emily added about his role of theoretical physicist J. Robert Oppenheimer.

“Of course he didn’t want to come and have dinner with us. He couldn’t. His brain was just too full,” Matt agreed during the cast’s group interview with the publication. Cillian concurred, saying, “You know that when you have those big roles, that responsibility, you feel it’s kind of overwhelming.”

The Dark Knight Rises star told GQ in a July 24, 2023, interview how the role in the Christopher Nolan-directed movie became all-consuming.

“Inevitably, if you play a character for a long time, and I was researching him for six months, then shooting it for however long that was … And you’re playing them 18 hours a day every day. By osmosis, you’re exchanging atoms, You become consumed or immersed [by it], that’s just the way it is,” he shared with the outlet.

Cillian also agreed with Emily and Matt’s assessment that he wasn’t very fun to be around during the production.

“It was a big part, and there were big, big questions that were grappling with, these huge ethical, moral questions. And Chris had written the script in the first person. So, I knew that a lot of the weight was on my shoulders, even though we have this incredible ensemble,” he explained.

“There was a responsibility that I felt about playing the part. That’s just the way I work. I get very consumed by the work, and I don’t really have time for hanging out. And in this movie, I was [regularly] skipping dinner, you know, so I wasn’t great craic to hang out with. But that’s just the way it was. It’s just the nature of the work,” Cillian added.