Paul McCartney, the up-and-comer who was recently featured on Kanye’s “Only One” and Rihanna’s “FourFiveSeconds,” just finished up a session with Lady Gaga and Mike McCready. Gaga posted some photos via Instagram earlier today of them recording together in the studio, including a group shot featuring the Pearl Jam guitarist. “Had a beautiful session with Sir Paul McCartney and friends,” Gaga wrote. (Why is she calling him sir?!) “Working on one of his many secret projects! Killer musicians, vibe, and lots of laughs.” In another caption, she said: “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!” Check out the other pictures from the studio below.

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.

A photo posted by @ladygaga on Feb 3, 2015 at 5:57pm PST

Studio rat house.

A photo posted by @ladygaga on Feb 3, 2015 at 7:42pm PST

[Photo via Instagram.]