So far this year, Paul McCartney has collaborated with rapper Kanye West and pop diva Rihanna. Now, he’s working with yet another chart-topping pop star: Lady Gaga.

Gaga posted a photo on Instagram of her and McCartney in the studio together, and wrote, “Always a good time with my buddy. I’ll never forget when he called me last year to work and I hung up the phone cuz I thought it was a prank!”

A second photo shows Gaga posing with McCartney and his band; she captioned that one, “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.”

McCartney will perform his collaboration with West and Rihanna, “FourFiveSeconds,” on the Grammy Awards this Sunday night.