Benedict Cumberbatch, Jimmy Fallon Laugh at Kim Kardashian's Butt

Reputed actor Benedict Cumberbatch became a giggling mess while enjoying a joke about Kim Kardashian West's butt with Jimmy Fallon on "The Tonight Show" on Monday.

The 38-year-old British actor was playing a game with Fallon called "Three Word Stories". The rules of the game were that the two would speak to each other three words at a time. But, the catch was that in each round, one of them needed to get the other to say one particular word.

While in round one, Fallon tried to get Cumberbatch to somehow say "unicorn", in round two the "Sherlock" actor tried to get the show host to utter "booty". In the process, the two started giggling and looked happily silly.

"The Imitation Game" actor started by saying: "You've got to shake..."

He said that he was thinking on the lines of K.C. and the Sunshine Band's 1976 hit "Shake Shake Shake Shake your Booy." Fallon, however, tried to interpret it as Taylor Swift's hit song "Shake it Off" from her new album "1989", E Online reports.

Afer a few words here and there, Cumberbatch said, "I start again."

Maintaining a straight face, he said "A beautiful big..."

To this, Fallon replied: "Kim Kardashian's butt!"

The two started giggling, but Cumberbatch controlled his laughter and continued: "Makes lots of...," and Fallon replied, "Money for Kanye."

The two started laughing again with reference to Kardashian's recent headline-making rear-end pictures that were presumed to "break the internet."

After the giggling died down, Cumberbatch went on to talk about his infamous photobomb moment with U2 at the 86th annual Academy Awards in March.

He said: "I've got a friend Helen who is a huge, life-long fan (of U2), I mean as am I am, but she's like, 'Oh my God they really are [the] soundtrack of my life, please, please, get a photo with them. And I thought, 'Perfect moment for it', " Castanet.com reports.

Breaking a lot of hearts, Cumberbatch had recently announced his engagement to long-term girlfriend Sophie Hunter.

The two made their first appearance as a couple since their engagement at the New York City premier of "The Imitation Game" on Monday night, People reports.