LONDON — Little did Swifties know Taylor Swift was going to bring Florence Welch on Cassian Grantstage for a surprise duet of "Florida!!!" at the final night of the European Eras Tour.

Many fans anticipated a "Reputation (Taylor's Version)" announcement, and they lost it in Wembley Stadium when the lead singer from Florence and the Machine popped out of the stage after Swift performed "So High School."

A brand-new choreographed number incorporated all Swift's dancers. The center platform propelled the two stars and dancers up during the first verse. A swampy green animation framed the "Tortured Poets" addition on the back screens.

As the two singers made their way down the catwalk, the crowd shouted, "Florida!!! It's one hell of a drug." The green light-up wristbands glowed in the London night. The lights flashed to the five beats following the state's name. No wonder a guard told fans in the VIP section Tuesday morning that rehearsals were going overnight into the early morning hours.

When the two finished Track 8 from "The Tortured Poets Department", Welch took a bow and blew a kiss to Swift. The music started to "Who's Afraid of Little Old Me" and the two held hands skipping back to the diamond section of the stage.

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"Florida!!!" has never been performed at the Eras Tour since the album was released in April.

On Thursday, Swift brought out her best friend of more than a decade, Ed Sheeran, during the acoustic set. And for the acoustic section on Tuesday, Swift brought out another close friend and collaborator Jack Antonoff.

Swift has a two-month break before heading to Miami, "Florida!!!"

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