During the New York City stop on Troye Sivan's
tour this week, pop's reigning twink brought out a very special guest onstage at Radio City Music Hall: Charli XCX. According to
, Sivan called XCX one of his "pop icons" and added that "she is the most creative and she is literally a fucking tastemaker -- she's at the forefront, you know what I mean?." The pair launched into the first live performance of their nostalgic new track "1999." Watch a clip below.