Katy Perry and Taylor Swift at the 52nd Annual GRAMMY Awards - Salute To Icons Honoring Doug Morris held at The Beverly Hilton Hotel on January 30, 2010 in Beverly Hills, California. Kevin Mazur/WireImage

After years of bad blood, Katy Perry opened up about her ongoing feud with Taylor Swift during a particularly honest edition of James Corden’s Carpool Karaoke, which aired on Monday, May 22. During her jam sesh with the late-night host, Perry, 32, revealed that she would like to move on only if T. Swift, 27, can apologize.

Here, Us Weekly looks back at how the pop superstars went from friends to, as Swift once put it, “straight-up enemies.”