It's a pretty big deal considering Charli is one of 2014's hottest artists - that and Gwen's failed to strike a chord with audiences with her recent jams.
"It was time for her to really express herself and not have a bunch of people telling her what to do," Pharrell says of Gwen. "I held up the mirror and [said], ‘Do you know who's in there? Do you know how many people respect that person?' The more she saw, the deeper she reached, and the crazier the stuff came out."
"She's an open book," says producer Benny Blanco. "She's cuckoo, she's a superhero, but there's vulnerability there. Even the biggest people [she worked with] were star-struck."
Are you ready for a Gwen Stefani and Charli XCX banger?