The beat goes on and on and on and on and... Taylor Swift added yet another member to her ever-growing squad on Saturday, Oct. 3, when she invited Charli XCX to join her onstage in Toronto for an epic duet.

The "Wildest Dreams" singer, 25, and the "Sucker" hitmaker, 23, got the crowd going with a rendition of the 2014 smash "Boom Clap," originally from the Fault in Our Stars soundtrack. Swift even trotted out a new outfit for the occasion — a multicolored sequined crop top and matching hot pants.

"BOOM. CLAP. @charli_xcx just killed it in Toronto," the 1989 headliner captioned an Instagram video of the performance, which featured some showy pyrotechnics and a lot of sass.

BOOM. CLAP. @charli_xcx just killed it in Toronto!!!

A video posted by Taylor Swift (@taylorswift) on Oct 3, 2015 at 7:48pm PDT

She later posted a photo of the pair posing back-to-back onstage, their hands raised triumphantly overhead. "@charli_xcx was incredible tonight," Swift wrote.

The British singer-songwriter (she penned Icona Pop's "I Love It") returned the compliment, sharing a picture of them backstage with the caption, "Thanks for having me tonight @taylorswift. P.S. My tour manager has the biggest crush on u ;)"

The "Break the Rules" songstress was just the latest in a very long line of musical guests on Swift's 1989 tour. Past performers include Justin Timberlake, Mick Jagger, Steven Tyler, John Legend, Nick Jonas, Alanis Morissette, Nelly, Keith Urban, Avril Lavigne, Selena Gomez, and Leona Lewis.

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