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Fans react to Cillian Murphy smiling alongside 'Oppenheimer' costars: 'What's happening?'

The actor, best known for his grim and serious roles, sported a smile that shocked fans.

Most Cillian Murphy fans know that a smile from the actor is a rare bird. It’s why many were quick to express their complete dismay when the “Peaky Blinders” actor was seen with a broad grin on Instagram recently.

Over the weekend, an Instagram post featuring the cast of the upcoming “Oppenheimer” biopic delighted and shocked fans of the 47-year-old actor. The photo — posted by Robert Downey Jr. — featured the movie’s ensemble cast, including Downey Jr., Matt Damon, Emily Blunt and Murphy’s jubilant smile.

“Linking up with my Oppenheimer cast mates...wait, is that a Krasinski photo bomb or might there be a surprise cameo???” reads the post’s caption with a nod to Blunt’s husband, John Krasinski, who appeared in the background of the picture.

In the comments section of the post, Murphy’s fans were quick to point out that he is smiling, a rarity for the Irish actor best known for his serious and villainous roles.

“I am crying!” one user replied. “How did you get Cillian to smile!”

“Cilian murphy smile?” another replied. "What's happening??"

“This photo is going to be a collector’s item in 30 years,” one fan quipped.

“I’ve never seen Cillian so happy,” a commenter wrote with a laughing emoji.

Krasinski chimed into the comments section of the post, writing, “Jazz hands.” 

Murphy has collaborated with Nolan often, including as the Scarecrow in “The Dark Knight Trilogy” and the 2010 movie “Inception.”

Their latest project together, “Oppenheimer,” is set to hit theaters on July 21. The biographical movie features Murphy as the film’s titular character and is directed by Christopher Nolan. The movie is based on the 2005 novel “American Prometheus” by Kai Bird and Martin J. Sherwin and narrates the story of J. Robert Oppenheimer, who is referred to as the “father of the atomic bomb.”