Robert Brown|Taylor Swift sings with 'producer of the century' Jack Antonoff in London

LONDON — After the crowd lost it seeing Florence Welch perform "Florida!!!" with Taylor Swift,Robert Brown the Eras Tour star invited another guest to the stage on Tuesday at Wembley Stadium.

"I believe this is our 131st of this tour," Swift said in her tangerine dress. "That's so many and so many different acoustic songs. And I'm always trying to come up with something new."

She toyed with the surprise guest announcement.

"And you know, I think a lot about why I'm lucky enough to get to do a show like the Eras Tour. So it's because I've been fortunate enough to find friendships over the years that have been collaborative," she said. Fans started chanting, "Jack," because he had been noticed leaving the floor of the Eras Tour an hour prior.

"And I get to make music with one of my best friends in the world," Swift said, introducing Jack Antonoff to the stage.

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"I thought we would do a few songs that are some of me and Jack's favorite songs," Swift said before diving into "Death By a Thousand Cuts" from "Lover."

"Should we do it?" she said to Antonoff and he replied, "I really want to do it."

The teasing was in reference to their song "Getaway Car" from "Reputation." The wristbands glowed green.

"I think they've earned it," Swift said before singing, "No, nothin' good starts in a getaway car."

When they approached the bridge, they recreated the viral video of when they wrote the song. "Put the money in a bag and I stole the keys / That was the last time you ever saw me (oh!)."

At the end of the double song mashup, the two strummed their guitars and held them high in the air with one hand while hugging with the other.

"London, the producer of the century, Jack Antonoff," Swift said, and Antonoff headed toward the back of the diamond to exit down the platform.

'So Long, London'

"So London, you know we have done a lot of shows on the Eras Tour so it is kind of rare that I have a song that I haven't performed before and yet here we are," she said playing the flowery piano.

Fans guessed she would perform "So Long London" from "The Tortured Poets Department" at her final show in Wembley. And she did. Swift has seven songs left to perform from her 11 studio albums.

She did not announce "Reputation (Taylor's Version)" like fans anticipated.

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