Lady Gaga reveals collaboration with Paul McCartney

Paul McCartney is certainly keeping busy. Just hours after the music video dropped for "FourFiveSeconds," his collaboration with Rihanna and Kanye West, Lady Gaga revealed she, too, is collaborating with the former Beatle.

"Had a beautiful session with Sir Paul McCartney and friends. Working on one of his many secret projects! Killer musicians, vibe, and lots of laughs," she captioned this Instagram photo:

She also uploaded this photo of their session, revealing that the first time Sir Paul called to work with her, she hung up thinking the call was a prank:

No word yet on what will result of their "secret project." But Lady Gaga is no stranger to collaborating with music legends. She released the duets album, "Cheek to Cheek," with Tony Bennett in 2014.