The American pop star has been tapped to perform during Sunday's concert on the grounds of Windsor Castle.
Blake Lively, Taylor Swift and Chrissy Teigen also sat out Monday's event.
Both judges are set to perform at King Charles III's coronation concert.
Luke Bryan chats with ET after 'American Idol's live episode on Monday, which aired on ABC.
Lionel Richie chats with ET after 'American Idol's live episode on Monday, airing on ABC.
Katy Perry chats with ET after 'American Idol's live episode on Monday, airing on ABC.
Perry and Richie will be in the U.K. to perform at the coronation concert.
The country star teased their replacements ahead of his Stagecoach gig.
Perry is just one of the performers set to take the stage at King Charles' coronation in London next month.
'American Idol' airs on Sundays and Mondays on ABC.
Orlando Bloom chats with ET at Sony Pictures' presentation at CinemaCon 2023 in Las Vegas about his movie, 'Gran Turismo,' out Aug. 11.
The singer also jokes with ET about her plans for the Met Gala.
Katy Perry chats with ET after the live taping of 'American Idol,' airing Sundays and Mondays on ABC.
A source tells ET Katy Perry is 'excited' to perform at King Charles' coronation and is preparing for the big day.
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