Haim and Taylor Swift performed "Love Story" and "Gasoline" at the O2 Arena in London, England.

Taylor Swift Crashed Haim's London Concert & Performed This Fearless Track

She dressed like a Haim sister too.

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Haim closed out the European leg of their tour with a bang. On Thursday, July 21, the band consisting of sisters Este, Danielle, and Alana Haim, performed at the O2 Arena in London. In the middle of their show, the women surprised the crowd by bringing out their long-time bestie Taylor Swift for an epic mashup of their song “Gasoline” and her song “Love Story.” Of course, fans were in shambles over the moment.

Swift appeared on stage wearing a black crop top and leather pants just like the Haim sisters have all tour. The singer told the audience she wanted to support the sisters on their One More Haim tour, so she decided to join them on stage for one of their biggest any friend might.

"I heard that my girls were playing in London at the O2 and I thought, 'I'm gonna have to see that,’ and it looks like there's about 20,000 other people that also thought that," she said in a video broadcaster Ryan Bailey on Twitter on July 21.

Swift then teased the songs they’d go on to perform. "We had a thought, that if we were to do some sort of mashup, we could possibly maybe get you to sing the loudest that you have sung all night, which is a tough challenge because you’ve been singing very loudly. It’s extraordinary work,” Swift said, before asking, “Would you sing with us?”

The crowd erupted in applause and Swift began performing her fan-favorite single “Love Story,” which appeared on her 2008 album, Fearless. Swift and Haim then integrated the track with “Gasoline.” The original version of the song was featured on Haim’s third studio album, Women in Music, Pt. III, which dropped in June 2020. A remix of “Gasoline,” featuring Swift, was released in February 2021, making the stars’ live collaboration that much more epic.

On July 22, the day after their show, Haim shared a backstage pic with Swift on Instagram. “Can’t get over last night, london ! thank u SO MUCH to our fourth sister @taylorswift for joining us on stage for our sold out show at the O2 arena!!!! GAHH!!!” they captioned the photo.

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Haim’s London concert marked their final European show as part of their One More Haim tour. Up next, the band is set to return to the United States for a series of concerts in Denver; San Diego; Nashville; Dover, Delaware; and Dana Point, California.

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If you’re like me and are having FOMO after watching Haim’s concert videos, remember that tickets to upcoming shows are still available.