Charli XCX joined the star for a live version of their summer hit Guess, a song which itself featured Eilish as an unexpected extra, adding her performance to the version featured on her Brat and It’s Completely Different but Also Still Brat remix album.

Billie Eilish surprised fans with Charli XCX on Tuesday to deliver the live debut of their “Guess” (Remix) in Los Angeles at the Kia Forum. On the third of five nights at the arena for Eilish, the pair took the “Brat”-green lit stage to sing their Grammy-nominated high-energy track.