Taylor Swift and Katy Perry seem to be in a feud, and it all started with John Mayer.

PageSix, during her new Rolling Stones interview, Taylor Swift mentioned an enemy that was her inspiration for her new song "Bad Blood".  Later on, Katy Perry tweeted
this which is believed to be a direct 'dig' at Taylor.

Oh, we’re just straight-up enemies. And it wasn’t even about a guy! It had to do with business.

In the interview, Taylor Swift had this to say regarding Katy Perry, "Oh, we’re just straight-up enemies. 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. I don’t think there would be any personal problem if she weren’t competitive.”

Of course the two stars both had previously dated John Mayer, and that may have something to do with the feud as well.

Taylor and John Mayer started dating in 2010.  After they broke up, she released the song "Dear John" that took major jabs at the singer about his manipulation of her and playing his "dark and twisted games".

Katy and John Mayer started dating in 2012.  That was when John admitted he was really humiliated by Swift's song.  After that, Katy slowly started to give Taylor the cold shoulder. Taylor also stated in the interview that she thought her and Katy were friends but at award shows, she always felt like Katy was insulting her.

It was also reported a while back that a few of Taylor's dancers left to go with Katy during her tour.

Unfortunately, reps for both singers weren't able to be reached for comment.