Lady Gaga and Bradley Cooper's chemistry lit up the stage at the 91st Annual Academy Awards Sunday night. 

The "A Star is Born" stars serenaded the world with a live performance of their nominated hit song "Shallow." It was Cooper's Oscar performance debut. 

It hasn't been the first time the breakout song has been performed live. Gaga sang it at the Grammys earlier this month, but Mark Ronson filled in for Cooper's role. Cooper, who did not know how to sing prior to filming "A Star is Born" first sang the iconic duet with Gaga at her Las Vegas show, "Enigma." 

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Cooper told E! News earlier this month that he was sure he'd be "terrified" to perform live at the Oscars. When describing his first live performance in Las Vegas, Cooper said he didn't want to "ruin" Gaga's show. 

"She just crushed it or two hours..and I thought, 'Please let me just be on pitch.'" 

Cooper and Gaga's performance hit all the right notes at the Oscars, and they received a standing ovation from the audience. Fans on Twitter also couldn't stop talking about their chemistry on stage.

"Shallow" won the Oscar for Best Original Song. Cooper was also nominated for Best Actor, Adapted Screenplay, and Best Picture (as a producer). Gaga was nominated for Best Actress.