Many people think Swift's 2014 revenge anthem "Bad Blood" is about Perry. Swift told Rolling Stone that year that the track is about a female artist, who she did not name.

"For years, I was never sure if we were friends or not," she said. "She would come up to me at awards shows and say something and walk away, and I would think, 'Are we friends, or did she just give me the harshest insult of my life?'"

Swift also told Rolling Stone that in 2013, the other singer "did something so horrible."

"I was like, 'Oh, we're just straight-up enemies,'" she said. "And it wasn't even about a guy! It had to do with business. She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me. And I'm surprisingly non-confrontational—you would not believe how much I hate conflict. So now I have to avoid her. It's awkward, and I don't like it."

A day after the article was published, Perry tweeted, "Watch out for the Regina George in sheep's clothing..."