Lady Gaga, Bradley Cooper perform surprise duet of 'Shallow' from 'A Star is Born' at Las Vegas show

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Fans in Las Vegas got a huge surprise on Saturday night during Lady Gaga's performance -- as Bradley Cooper came out on stage to perform a surprise duet with her of "Shallow" from their film "A Star is Born."

FOX 5's Kevin McCarthy was in the audience with his wife Lauren at Gaga's 'ENIGMA' show at the Park Theater at Park MGM.

The crowd went wild when Cooper, who directed and co-starred in the Oscar-nominated film with the pop star, appeared on stage.

Cooper stars as fictional country singer Jackson Maine, who discovers and falls in love with a young singer and ingenue named Ally, whom he takes his under his wing as a performer.

The film has been nominated for eight Oscar awards, including Best Picture, Best Adapted Screenplay, and cinematography.

Cooper is up for Best Actor, and Gaga for Best Actress, plus "The Shallow" is nominated for Best Song.

McCarthy, a huge fan of the film, called the performance "insane," and said they were even sitting in front of Cooper in the audience.

"What an amazing show. Cooper was sitting right behind us. We said hi a couple times. I was wearing a Jackson Maine shirt. Wow. Amazing seeing them do that live."

Watch the videos Kevin captured and check out Kevin's interview with Cooper and Gaga on the film in the player above.