Watch Billie Eilish And Charli XCX Perform “Guess” Together For The First Time

Today happens to be Billie Eilish's birthday. She's 23 years old now. That's fucked up, right? She's a major part of the pop establishment, and she is only now old enough to rent a car. What the fuck are the rest of us doing with our lives? Anyway, Eilish gave herself a birthday present last night. She was in the middle of a run of shows at Inglewood's Kia Forum -- her hometown arena, more or less -- and she performed the "Guess" remix with Charli XCX for the first time.

Charli and Billie released the delightfully trashy "Guess" remix back in August. The song was a #1 hit in the UK, and it reached #12 over here, which makes it Charli's biggest Hot 100 hit since "Boom Clap." Eilish has been performing the "Guess" remix by herself on her current arena tour. Last night, Charli came up on one of those little stage elevators, and the two did the track together, with a very fired-up crowd singing along. Eilish was wearing a gigantic Ecko shirt, and Charli was not. Watch it go down below.