By Nick Romano
June 23, 2018 at 04:19 PM EDT
Gareth Cattermole/TAS18/Getty Images

Taylor Swift‘s tours are always star-studded affairs, and her stops for Reputation are proving to be no different. When the singer behind “Look What You Made Me Do” hit London, she brought with her a surprise in the form of Niall Horan.

The former One Direction singer surprised the crowd gathered in the city’s Wembley Stadium Friday night, the first of two London tour dates, with a performance of his song “Slow Dance.”

The 24-year-old Irishman follows appearances by Selena Gomez, Shawn Mendes, and Troye Sivan, who all popped in for performances along the way on the Reputation tour.

Fans, obviously, flipped.

After the appearance, Swift shared behind-the-scenes photos of their “soundcheck at Wembley Stadium” to social media. “THANK YOU for surprising the crowd tonight!!!,” she wrote on Instagram.

Horan returned thanks to Swift “for having me last night at Wembley.” He added, “What a fantastic experience to share the stage with you!”

Watch clips of the performance above.