The actor, who directed and starred in the film which has been nominated for eight Academy Awards, sang the first half of the song while Gaga knelt at his feet. Bradley sat on a stool while Gaga leaned on his knee, looking up to him.
"So I'm gonna be a little chance-y..."
During Gaga's Saturday night performance of her Las Vegas residency, the artist called her Star Is Born co-star and director up on stage to deliver a rendition of the duet that's been stuck in my goddamn head since what feels like 2015.
"To have a voice like that in a song that you write is a dream come true", said songwriter Natalie Hemby, one of the song's co-writers.
The two locked eyes during the performance of Cooper's verse, with Gaga eventually looking at the crowd with a smile as if to say: "Can you believe he just did that?" Despite a rocky start in which the actor joked about having to adjust his in-ear monitor - "Jackson never used these", he quipped - the rest of the emotional number went smoothly. The song is also slated to be performed at the Oscars in February.
The singer then took a seat at the piano and began playing as Cooper stood up and leaned over the instrument, joining her in singing the chorus.