The cat's out of the bag. Taylor Swift did an interview with Rolling Stone and revealed that her song, "Bad Blood," from her upcoming album is about a falling out she had with a female singer. Swift referred to the mystery singer as a "straight up enemy" but didn't want to divulge the name.

Well, according to new reports Swift was taking jabs at pop star Katy Perry in the song.

"For years, I was never sure if we were friends or not," she told the magazine. "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?' [Then last year] she did something so horrible. I was like, 'Oh, we're just straight-up enemies.' And it wasn't even about a guy!"

Shortly after the interview was published, Perry took to Twitter to call out a mean girl, writing, "Watch out for Regina George in sheep's clothing." Many people assumed the tweet was aimed towards the "Red" singer.

According to TMZ, the feud has something to do with Perry supposedly "stealing" three of Swift's backup dancers. A source told the site that Swift felt betrayed because she had grown really close with the dancers and considered them to be her extended family.

However, the dancers were originally working with Perry but found work elsewhere when the "Roar" singer's tour ended a few years ago. That's when the three dancers started performing on the road with Swift.

The source told the site that the dancers were upfront with Swift and told her they did not want to sign on for a full tour and also wanted a 30-day by out. Once Perry announced she was going on tour again, the dancers reportedly gave Swift their 30-day notice but she got angry and fired them. According to TMZ, this all happened last year.  

Page Six reports that Swift and Perry's hatred towards each other goes back even further than that, to when Perry was dating John Mayer. Swift and Mayer briefly had a fling back in 2010 but he broke it off. In 2012, he started dating the "Fireworks" singer.

Swift is known for writing songs about past relationships so she penned a song about Mayer, titled "Dear John," and talked about how he played with her heart.

"Don't you think 19's too young to be played by/Your dark twisted games," she sang.

A source told Page Six that Mayer was "really humiliated" by the song and apparently Perry was none too pleased about it either.

"[Katy] started making digs at Taylor from then on," the source said.