The pair's appearance on the show comes after 'Idol' judges Katy Perry and Lionel Richie performed at the coronation concert Sunday.
Luke Bryan is joined by guest judges Ed Sheeran and Alanis Morissette.
The singer was one of the guest performers during the official coronation concert on Sunday.
The singer was spotted wandering around Westminster Abbey as she looked for her place on Saturday morning.
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.