Sigrid said she was “not feeling well” after playing the main stage of TRNSMT on Saturday afternoon.
The Norwegian singer described the performance as “really fun”, but said the heat had taken its toll.
Festival-goers faced temperatures of up to 30C at Glasgow Green, made all the hotter by dancing and jumping.
But despite the high temperatures, which are set to continue into Sunday, Sigrid gave TRNSMT a thumbs up.
“It was really fun,” she told the PA news agency. “It was incredibly hot.
“I’m still a bit like, honestly, I gotta admit, I’m not feeling very well.
“I’m okay, but it’s I’m not used to the heat. But it was great. The crowd, was really, really lovely.
“I was very impressed by how they braved the heat. This is probably one of the hottest shows we’ve ever done.”
The Strangers singer added: “It was really tough. This is one of the few shows where I’ve not been moving that much.
“It felt a bit like I should have given more but I just wasn’t able to. But it was really really fun and it was really nice to see Glasgow again.”
The pop star spoke as The Kooks played their set on the main stage in the background.
She said the band was fundamental to her learning music from a young age.
“That was my whole childhood, or my whole youth” she said as the indie band played Sofa Song.
“Seaside, I remember I covered that song.
“And She Moves In Her Own Way is one of the first songs I learned on guitar.”
She added: “The Kooks were so integral to me learning instruments.”
She said TRNSMT was one of her favourite festivals, adding that it was “amazing” and getting “better and better” every year.
She described Scottish crowds as “amazing, and very loud, rowdy”.
“I feel like in Scotland people are rooting for me,” she said.
“Today, I honestly was wondering am I gonna faint soon.
“If it’s not me surely someone in the audience must faint. Earlier today, I just felt they were rooting for everyone to do well.”
The Norwegian artist said she went to a farm near Glasgow before the festival to try some Scottish foods.
The singer said she had tried haggis before in Scotland, which she described as “weird”.
She had also tried Buckfast which she said was “intense”.
“I just got handed Buckfast once when we were playing Usher Hall,” she said. “It was quite nice.”
Crowds will hear Fontaines DC perform on Saturday night before Biffy Clyro close out the show.
Fans will hear Gracie Abrams on Sunday night before Snow Patrol performs the final set.
