Cillian Murphy took an extreme approach to dieting in order to transform into scientist J. Robert Oppenheimer for the Christopher Nolan-directed “Oppenheimer” film.

“He had such a monumental undertaking,” the actor’s onscreen wife, actress Emily Blunt, told Extra in a new interview.

“And he could only eat, like, an almond every day. He was so emaciated.”

Blunt’s comments on Murphy’s pre-filming eating habits bore an eerie resemblance to her famous line in “The Devil Wears Prada,” where her character, Emily Charlton, tells colleague Andrea Sachs (Anne Hathaway), “I’m on this new diet. Well, I don’t eat anything, and when I feel like I’m about to faint, I eat a cube of cheese.”

Her character then joked, “I’m just one stomach flu away from my goal weight.”

In “Oppenheimer” – which hits movie theaters Friday – Blunt, 40, plays the role of Oppenheimer’s wife, Kitty. The famous physicist Murphy portrays has been dubbed the “father of the atomic bomb” and was the director of the Los Alamos Laboratory during World War II.

Murphy, 47, has previously discussed his commitment to weight loss for the movie role.

“I love acting with my body, and Oppenheimer had a very distinct physicality and silhouette, which I wanted to get right,” he 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.”

However, Murphy made it clear that his dieting tactics aren’t safe and should not be replicated by others.

“You become competitive with yourself a little bit, which is not healthy,” he told The Guardian in July, adding, “I don’t advise it.”

The “Peaky Blinders” actor also explained that he didn’t want to disclose what foods his nutritionist suggested he cut out to slim down – or how much weight he lost for the part.

“I don’t want it (the headlines) to be, ‘Cillian lost X weight for the part’,” he admitted.

Like her co-star, Blunt appears to have also made some type of physical transformation ahead of the “Oppenheimer” debut. Page Six reported earlier this month that several fans believe Blunt may have underwent cosmetic surgery for a fresher facade during her press tour.

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“Is it just me or does Emily Blunt’s face look different?” one fan asked on Twitterwith another inquiring“Did Emily Blunt have some sort of surgery? Her face looks different…”

“I’m more concerned with Emily Blunt and the filler she put on her face. It looks like Madonna,” another argued.

Blunt also made headlines last week when she announced she was taking a step back from her acting career to spend more time with her family.

“This year, I’m not working. I worked quite a bit last year and my oldest baby is 9, so we’re in the last year of single digits,” she said during an interview on iHeart’s “Table For Two with Bruce Bozzi” podcast.

Blunt later clarified that reactions to her acting break were “overblown” and that she’s just taking a few months off to spent time with her husband, John Krasinski, and their two daughters: Hazel, 9, and Violet, 6.

“I was just taking some downtime — not quitting Hollywood,” she said at the London premiere of “Oppenheimer.”