Taylor Swift Plays ‘thanK you aIMee,’ ‘Castles’ With Hayley Williams

London is a “special” place to bring The Eras Tour, Taylor Swift said during her acoustic set at Wembley Stadium Saturday night (June 22).

At the second of three shows this weekend, the pop star decided to perform a song she’d never played live before. She also welcomed Hayley Williams to the stage for a duet.

“We get to play Wembley Stadium eight times this summer. When I’m thinking about that, you think about just being grateful and being thankful,” Swift told the crowd, showing appreciation for their support. (She’s got her trio of concerts in London this weekend, and she’ll return to Wembley for five additional shows later this summer, from Aug. 15-20.)

“On the other hand,” commented Swift, who was about to deliver the first of the night’s two surprise song performances, “it really makes me think about how every time somebody talks s— it just makes me work even harder.”

“I’ve never played this one before. Wish me luck,” she said, and then on acoustic guitar launched into “thanK you aIMee,” from The Tortured Poets Department: The Anthology. It marked the first-ever live performance of the track that has her singing, “All that time you were throwin’ punches, I was buildin’ somethin’/ And I can’t forgive the way you made me feel/ Screamed, “F— you, Aimee” to the night sky as the blood was gushin’/ But I can’t forget the way you made me heal.”

“I don’t think you’ve changed much/ And so I changed your name and any real defining clues/ And one day, your kid comes home singin’/ A song that only us two is gonna know is about you,” she adds in a later verse.

Swift performed “thanK you aIMee” as a mashup with Speak Now‘s “Mean,” another song about how she’s triumphed over naysayers.

“Someday I’ll be singing this song at Wembley,” she quipped, singing an improvised line to the melody of “Mean.”

To top off that moment Saturday night, she brought out Hayley Williams (who had opened the show with Paramore earlier) for a live duet of “Castles Crumbling,” their collaboration from the Speak Now (Taylor’s Version) vault. Swift and Williams sat side-by-side at the piano as they sang.

Swift recalled the last time they’d played live together: on The Speak Now Tour, when she welcomed Williams to the stage to perform Paramore’s “That’s What You Get” with her at a 2011 Nashville date.

Below, watch clips of Swift’s surprise song set from night two at Wembley. Stay up-to-date with the complete list of surprise songs she’s played on The Eras tour here.