Prince William just might be a Swiftie.

The royal celebrated his 42nd birthday on Friday night by attending the first London stop of Taylor Swift‘s Eras Tour, along with children George and Charlotte. He then posted a photo of them taking a selfie with the pop star on social media

riting: “Thank you @taylorswift13 for a great evening!”

Swift also posted a selfie from the meet-and-greet, which also included her boyfriend Travis Kelce. “Happy Bday M8! London shows are off to a splendid start,” Swift wrote.

Friday night’s show was the first of three at London’s Wembley Stadium. During the surprise song segment of the performance, Swift delivered the live debut of “Tortured Poets Department” track “The Black Dog” — named after a pub in Vauxhall — which was mashed up with “Come Back Be Here” and “Maroon.” She also played a medley of “Hits Different” and “Death by a Thousand Cuts.”

During the “1989” era of the show, Prince William was spotted dancing and singing along enthusiastically to “Shake It Off,” spurring chatter on social media. “That’s our next King of England and I’m so here for it,” one user wrote. Though his wife, Kate Middleton, recently made her first public appearance since her cancer diagnosis at last weekend’s Trooping the Colour event, she was not in attendance at the concert.

Other celebrities in attendance included “Bridgerton” star Nicola Coughlan; Cara Delevingne, who is currently leading the West End production of “Cabaret”; and “Queer Eye” breakout Jonathan Van Ness.

After this month’s dates, Swift will return to Wembley Stadium in August for five more shows to end the European leg of the Eras tour.