Karen O was forced to cancel her appearance at Olivia Rodrigo's Daisy Chain Fields festival at the weekend due to a "family emergency".
On Sunday morning, the Heads Will Roll singer took to social media to explain her absence.
"I was unable to perform at Daisy Chain due to a family emergency," she wrote. "Very sad to miss such a herstoric music event, but I'm where I'm most needed, with family back east."
The singer continued, "So much gratitude to Olivia for her advocacy for women, by women, who totally rock."
The Yeah Yeah Yeahs singer was billed as a special guest for the inaugural Irvine, California festival. Stevie Nicks and Sarah McLachlan, the other special guests on the lineup, joined Rodrigo onstage during her headlining set.
A previously unannounced Alanis Morissette performed Ironic alongside Rodrigo during the set, with Karen O missing the gig entirely.
Rodrigo acknowledged Karen O's absence during the headlining set before introducing Morissette as a surprise guest. "The bad news is that unfortunately Karen O is not able to make it tonight, I'm so sad," she said.
"She was so excited to come, she was one of the first people to say yes to Daisy Chain. But unfortunately she had an unexpected personal matter that requires her to be elsewhere. But let's send her a bunch of love, all of us, collectively. I love her so much."
Karen O is married to English film director Barnaby Clay, and they have one son together.
