She also covered the band's hit "The City."

Taylor Swift should not be left to her own devices — after all, she may just show up at a concert unexpectedly and perform.

Such is what happened on Thursday in London at The O2, where fans were gathered for the 1975's concert. According to videos shared by onlookers, Swift showed up unannounced onstage to give the first live performance of "Anti-Hero" from her latest album Midnights. Swift also treated the crowd to a rendition of the 1975's "The City."

The surprising cameo caps off a few months of mutual public admiration between Swift and the English synth-pop band. In November, the 1975's Matty Healy said in an interview that Swift had heard their new record, Being Funny In a Foreign Language, before its release. (Frequent Swift collaborator and Midnights producer Jack Antonoff also produced the 1975's album).

When asked if Swift returned the favor, Healy said that in fact, he and his bandmates had worked a bit on Swift's album, but whatever they made didn't make the final cut.

"We actually worked a bit on that but then the version of it never came out," the star said in an interview with KROQ's Klein/Ally Show for Audacy's DTS Sound Space. Though he didn't specify what they worked on or why it didn't work out, he did clarify, "it was for reasons that are not to be criticized" and he praised Swift, calling her "amazing."

Just days after the Oct. 21 release of her 10th studio album, Midnights, Swift shattered streaming and sales records left and right, including becoming the first artist in history to claim all top 10 spots on the Billboard Hot 100 in a single frame. The album, which sees the singer reminisce on sleepless nights throughout her life, marked both a return to pop and a return to more personal subject matter for Swift.

In addition to surprising fans at concerts, Swift is currently hard at work prepping for her massive Eras Tour, which kicks off in Glendale, Ariz. on March 17.

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