"I was freaking out," said Charli, who also co-wrote one of the biggest underdog pop hits of recent, Icona Pop's "I Love It." "I didn't even want to go to the session I was so excited. I was so worried I would f**k it up� I was doing some stuff for that yesterday actually. Who knows how it will go. We've written one song and it's a great track and if she likes it then amazing. It was just an honor to be asked."

Hayley Williams and the rest of Paramore recently asked Charli to ditch her U.S. dates and come open for the band in her native UK, another sign Charli's star is on the rise.