Taylor Swift just gave the debut performance of her number-one single "Anti-Hero."

The Midnights legend, 33, unexpectedly appeared on stage at The 1975's performance on Thursday in London (January 12).

Anxious followers flocked to social media to gush over the shocking cameo.

Taylor took the stage wearing a short silver dress and holding a guitar.

She gave the audience a stripped-down performance of the song. Videos from the performance show that concertgoers were singing along.

Taylor also delivered a cover of The 1975‘s “The City.”

Recently, "Anti-Hero" tied a record for her longest-running No. 1 song when it topped the Billboard Hot 100 for a seventh week, according to Billboard.

It’s a very safe bet that Taylor will perform the hit when she embarks on her Eras Tour later this year.