Los Angeles, April 30 : Singer Katy Perry is expected to be temporarily replaced on 'American Idol' by a "big-time" star. The 38-year-old singer and her "American Idol" co-star Lionel Richie are both scheduled to perform at King Charles' coronation concert in May, and Luke Bryan has told fans to expect some big-name replacements on the TV show, reports aceshowbiz.com. "It's big time. It's big time. The people that we have filling in, contestants have used their songs many, many times. A lot more than mine!" Luke, 46 - who has been a judge on the show since 2018 - told Entertainment Tonight. Katy and Lionel, 73, will both perform at the much-anticipated concert on the grounds of Windsor Castle. And Katy recently revealed that she's "so grateful" to have been invited to sing at the upcoming event. The pop star is already an ambassador for one of the monarch's charities, and she's now looking forward to the concert. Speaking about her invite, Katy told ExtraTV, "It was very regal, it was like a cursive I have never seen. I loved it. It was so beautiful and it was so grateful to get the honour because actually I am an ambassador for the British Asian Trust, which primarily focuses on ending child trafficking, which is a huge issue of our time and it just aligned with all my values." "I'm also an ambassador for Unicef. And as a mother I know first-hand these innocent children need help, they need to be helped. So I'm just going there as an ambassador and they asked me to sing and it all aligned." Meanwhile, Orlando Bloom thinks it's "cool" that Katy will perform at the coronation concert. The 46-year-old actor - who has Daisy, two, with the pop star - is already looking forward to seeing Katy perform at the historic occasion. Orlando - who also has Flynn, 12, with his ex-wife Miranda Kerr - told Entertainment Tonight, "My girl's gonna be singing, that's fun. I'm not gonna make it there, sadly, but she's representing which is cool. She does those big, historical things. It's wonderful. She sang for the president too. She does that." /IANS