Cillian Murphy's role in "Oppenheimer" pushed him to extreme lengths.
In fact, his co-star Emily Blunt — who portrayed Murphy's wife Kitty Oppenheimer — revealed that the "Inception" actor underwent a drastic transformation to play the role of J. Robert Oppenheimer, the father of the atomic bomb.
"He had such a monumental undertaking," she told Extra in an interview published July 7. "And he could only eat, like, an almond every day. He was so emaciated."
Murphy previously admitted that he was committed to a strict diet for the role in order to accurately capture the scientist's appearance.
Get a weekly recap of the latest San Francisco Bay Area housing news. Sign up for NBC Bay Area’s Housing Deconstructed newsletter.
"I love acting with my body, and Oppenheimer had a very distinct physicality and silhouette, which I wanted to get right," Murphy told the New York Times in May. "I had to lose quite a bit of weight, and we worked with the costume and tailoring; he was very slim, almost emaciated, existed on martinis and cigarettes."
Check Out the Most Surprising Celeb Transformations of the Week
Entertainment News
However, he warned that the undertaking was not something he would recommend to others.
"You become competitive with yourself a little bit, which is not healthy," the "Peaky Blinders" actor told The Guardian in July. "I don't advise it."
As for how much weight he lost? Murphy opted not to share a number, explaining, "Ach, no. I don't want it to be, 'Cillian lost x weight for the part.'"
In addition to his physical transformation, the 47-year-old said the fast-paced filming process allowed him to embrace the character a lot more.
"It's like you're on this f------ train that's just bombing," he told the outlet. "It's bang, bang, bang, bang. You sleep for a few hours, get up, bang it again. I was running on crazy energy; I went over a threshold to where I was not worrying about food or anything…But it was good because the character was like that. He never ate."
Oppenheimer hits theaters July 21.
