Katy Perry was a regal firework duringKing Charles III's coronation concert!On Sunday, the judge took the stage for a performance in honor of the new king at Windsor Castle. For her set, Perry performed her hits, «Roar» and «Firework.»Starting things off the castle's steps, Perry was shined bright as ever in a big gold ballgown as she made her way to center stage.The royal family got in on the fun, with Prince William and Kate Middleton's daughter, Princess Charlotte adorably singing along. Before singing «Firework,» Perry addressed the crowd and thanked the newly crowned king and queen for allowing her to be there but also for the work she's been able to do on behalf of the crown via the British Asian Trust and their children's protection fund.«Thank you for bringing out the firework in so many young people,» Perry said.Ahead of the special concert, Perry dished to ET about the opportunity to have a part in the festivities. «I'm grateful I get to go.