Katy Perry says one of her biggest regrets is turning down a Billie Eilish collaboration.
The 38-year-old singer revealed she was approached about working with Billie, 21, before she became a huge star but Katy turned down the offer.
In a TikTok posted by 102.7 KIIS FM, Katy can be seen explaining: "Someone sent me an email one time that was: 'Hey, check out this new artist. I'd really like us to work with her because she was working with me for Unsub [Records].
"It was a song called 'Ocean Eyes,' and it was just a blonde girl. And I was like, 'Meh, boring.'
"Big mistake. Huge mistake. Don't let this hit the Internet."
Eilish went on to find fame in 2015 with 'Ocean Eyes' and has since won seven Grammy Awards and a Golden Globe Award and Oscar for Best Original Song.
Katy appeared in Billie's 2021 documentary, 'Billie Eilish: The World's A Little Blurry', when she revealed her partner Orlando Bloom was a huge fan.
Katy told Billie: "My fiancé who doesn't listen to modern music, he'll only play you in the car all the time."
She added: "Congrats, I'm so proud of you. I wanted to say, this is going to be wild for 10 years. If you ever wanna talk… 'cause it's a weird ride."