During her set at the show attended by the newly crowned King Charles III, the 38-year-old star sang some of her biggest hits.
The 20,000-strong audience was singing along to the incredible performance when some fans watching at home noticed a very awkward moment.
During her rendition of Firework, Perry sings the lyrics: “You just gotta ignite the light / And let it shine / Just own the night / Like the Fourth of July.”
July 4 is American Independence Day, marking the date the Founding Fathers signed the Declaration of Independence to secede from King George III’s British Empire.
The American Revolutionary War had been raging for a year and would go on until 1783 when George Washington’s forces defeated the British.
One fan tweeted: “Katy Perry reminding to ‘own the night like the 4th of July’ … Um, is that awkward?”
Another wrote: “This Coronation Concert is lit – but the irony of Katy Perry singing firework which references celebrating July 4th … To the King of England.”
Another fan wrote: “Not sure Katy Perry should really be mentioning the 4th of July in front of the King.”
Further on in the performance, Perry actually ended up leaving the month out of the lyrics.
A viewer tweeted: “Not Katy Perry skipping the word July in the lyrics ‘fourth of July’ for King Charles.”