The singer was one of the guest performers during the official coronation concert on Sunday.
On Sunday, the American Idol judge took the stage for a performance in honor of the new king at Windsor Castle, performing her hits, "Roar" and "Firework."
Starting things off the castle's steps, Perry shined bright as ever in a big gold ballgown as she made her way to center stage, getting not just the crowd but the royal family in on the fun, with Prince William and Kate Middleton's daughter, Princess Charlotte adorably singing along.
Charlotte enthusiastically belted out the lyrics to the inspiring track, as she waved her union jack flag from side to side with her mom, Kate, also bobbing her head along to the music.
Princess Eugenie also seemed to be loving Perry's performance, as she was seen, not far behind Charlotte, singing and waving her flag as well.
Before performing "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. I met His Majesty-to-be a few years ago and he named me as one of the ambassadors to his organization, The British Asian Trust, which is an organization that helps fight to end child trafficking," Perry told ET last month.
"So I'm also an ambassador for UNICEF, and it really aligned with my values. That's mostly why I'm going, to be an ambassador and to say, 'Hey, this is me from the USA.' No, but it's so cool," she added.
Perry was in good company as fellow Idol judge Lionel Richie performed as well, getting the audience on their feet with renditions of his hits "Easy (Like Sunday Morning) and "All Night Long," which even saw Charles show of some of his moves.
The televised concert comes one day after Charles and Camilla were officially crowned during the historic coronation ceremony.
King Charles III's coronation took place at Westminster Abbey and formalized his role as the head of the Church of England and marked the transfer of his title and powers. It was also the official moment he is crowned king.
King Charles was crowned with the St Edward's Crown from the 17th century, which weighs nearly five pounds, has a solid gold frame and 444 stones.
Meanwhile, his wife, Camilla Parker Bowles, was anointed and crowned as queen. Camilla is the first divorcee to be crowned, and the coronation invitation that was released in April made headlines when it referred to her as Queen Camilla for the first time. Until then, she was described as queen consort.
As for Prince Harry, he attended the coronation, but his wife, Meghan Markle, did not join him. This news came amid tension within the royal family after the December release of Harry and Meghan's Netflix docuseries, Harry & Meghan, and the Duke of Sussex's bestselling memoir, Spare, which came out in January. Both the doc and the book were critical of Harry's family and also shared intimate details about the royals from the couple's perspective.
While Harry was in England, Meghan stayed at their home in Montecito, California, with their two children -- son Archie, who turned 4 on the day of the coronation, and 1-year-old daughter Lilibet. Despite Harry and Meghan's estrangement from the royals, the couple was featured in the official souvenir program celebrating the coronation, which included a happy photo of the family -- including William, Kate, Charlotte, Prince George and Prince Louis -- celebrating King Charles' 70th birthday in 2018.