Last night, Prince William celebrated his 42nd birthday by attending the pop star's sold-out Eras Tour performance at Wembley Stadium with his two eldest royal children ... George and Charlotte.

Check out the footage ... one of Taylor's gazillion fans used a cell phone camera to capture the prince rocking out to her famous tune, "Shake It Off."

Based on the visual evidence, William has some pretty intense dance moves, shimmying his hips wildly with his arms spread wide open.

And, it looked like his kids were having a blast too, but they weren't as animated as William.

Meanwhile, Taylor showed how much she adored her boyfriend, Kansas City Chiefs tight end Travis Kelce, as she cranked out her hit, "So High School."

While onstage, Taylor imitated an archer pulling back on a bow with an arrow, which is the same move Travis unleashes whenever the Chiefs score a touchdown at Arrowhead Stadium.