Taylor Swift thrilled fans in Washington, D.C. on Monday night (13Jul15) by performing Royals with her pal Lorde during a gig in the city.

The Love Story singer later informed fans that the New Zealand-based star had flown in especially for the show.

She tweeted, "When your friend flies across the world to surprise your crowd with 'Royals' bc (because) she's a wondrous angel."

Lorde responded, "but seriously, @taylorswift13 is the leader of a great and beautiful galaxy that i'd live in forever."

Both pals posted photos of their onstage get together and Lorde added, "just laughing like 'this is our job how lucky are we/this stadium is so loud and pretty/we are best buds/KILLING IT."