See exclusive images of Lady Gaga and Bradley Cooper in A Star Is Born  

This is the first time the pair sing onstage together and is highlighted in the film's trailer. All of Born's music is sung live and was a collaboration between Cooper, Gaga and music industry vets, like Mark Ronson, Jason Isbell, Lukas Nelson, Dave Cobb, Paul Kennerley and Hillary Lindsey.

Cooper's rock star plays a song for his beloved, who has undergone a pop star makeover. The first time Gaga and Cooper sang together in real life was at a piano in Gaga's house. "I remember I stopped playing, and I was like, 'Oh my gosh, Bradley, you can sing,'" she says.

Cooper chose comedian Chappelle, who plays Jackson's pal Noodles, for a pivotal dramatic role. "Dave Chappelle is somebody I find magical," says Cooper. "I was doing a play in London and he came and we hung out all night. I spent two years trying to get him [for Born]."

The performances in Born were shot at actual music festivals like Glastonbury, Stagecoach, and Coachella. Unlike most musicals, the vocals were recorded live. "I was so excited that he wanted to do all of the music live and record our voices live," says Gaga. "It was a dream come true. It's my least favorite thing when I'm watching a movie when someone starts singing to playback and they're lip-synching."

A Star Is Born is filled with huge musical performances but the heart of the story is the tumultuous, tragic romance between Jackson and Ally. "I always wanted to tell a love story," admits Cooper. "There's nothing better, for me, cinematically than to be able to tell a love story, like a real love story, a broken love story."

Jackson and his brother Bobby, played by Sam Elliott, have a volatile, jealousy-fueled relationship in the film and several heartbreaking moments. Cooper pitched the role and movie to Elliott over dinner. "I pitched him this whole idea about how this young musician had this older brother and he wanted to be him so much and he kind of took his voice. But Sam's character also wanted to be a musician and envied the fact that Jackson had this talent of songwriting."

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