Oscars 2019: Lady Gaga on performing 'Shallow' with 'A Star is Born' co-star Bradley Cooper

Lady Gaga and Bradley Cooper brought a star-studded audience to their feet as they performed their Oscar-winning song, "Shallow," at the the 2019 Oscars on Sunday night.

"I rarely relinquish control and I was like, 'Bradley, this one's on you.' And he had a beautiful vision for what he wanted, and so all of that camera movement and everything that you saw, it was from him," Gaga told "Good Morning America's" Lara Spencer backstage about Cooper.

"The truth is that this song wouldn't have won tonight and this song wouldn't wouldn't be what it is without him," she added.

The "A Star is Born" co-stars sang the duet on stage just before "Shallow" nabbed the award for best original song. Lady Gaga, co-writer Mark Ronson and others took the stage to accept the trophy.

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Gaga thanked Cooper when she accepted the Oscar during her tearful speech.

"Bradley, there is not a single person on the planet that could sang this song with me but you," Gaga said on stage. "Thank you for believing in us."

Gaga told "GMA" that "Shallow" wasn't always meant to be a duet, but Cooper, the film's director, thought differently.

"We felt that it would be a great duet and he thought so as well," she said. "I sung with a lot of people and I really meant what I said tonight. No one could've sang that song but him."

When accepting the award, Gaga mentioned in her speech that success isn't about winning, but about not giving up.

"I don't remember what I said," she told "GMA," laughing. "It's a dream sequence and all that you could hope for is that you say something that will reach people -- that they will feel inspired because when you win, it's not about us. It's about what we can give to the world."