Right now, Troye Sivan and Charli XCX are operating on the outside fringes of mainstream pop stardom, but they’re the ones who are really doing fun, inventive, exciting things with the form. And now they’ve teamed up. On Friday, Sivan and Charli released the collaboration “1999,” a fizzy dance-pop jam that manages to be nostalgic for the peak-teenpop era. And last night, they performed it live for the first time.

Sivan has lately been touring some big rooms behind the release of Bloom, his excellent new album. And last night, he headlined Radio City Music Hall, one of our most storied live venues. Toward the end of the set, Sivan brought out Charli as a surprise guest, and they proceeded to perform the living hell out of “1999.”

“1999” is a dizzily fast song, and to perform it, you really need to bring energy. Sivan and Charli both had that. They also seemed to love being onstage together, and they’d clearly had at least one quick conversation about choreography. All of this is good. This is how it should look when one pop star shows up on another pop star’s stage. Watch a couple of fan-made videos below.

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@charli_xcx came onstage and they sang 1999!!

A post shared by Hannah🌺 (@troyevideos_) on Oct 10, 2018 at 3:12am PDT

“1999” is out now at the streaming services.