After word got out that Katy Perry and Taylor Swift might be straight-up enemies, it appears that one of the reasons for this could be due to a certain ex-boyfriend that the two singers share.

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On Tuesday, Page Six mentioned how Swift dated John Mayer in 2010. After they broke up, she released a song called "Dear John," and that apparently made him feel "really humiliated." Mayer eventually dated Perry although that didn't work out either. Even though the two broke up, it looks like the "Birthday" singer may have been giving Swift a hard time.

"Perry started making digs at Taylor from then on," music sources told the site. And from the looks of it, this may have started happening when Perry and Mayer began their relationship.

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The alleged feud between the two girls started when the "Shake it Off" singer dished on the inspiration for the song "Bad Blood" where it seems like another singer did something wrong.

"It had to do with business," Swift told "Rolling Stone," published on E! News. "She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me."

On Tuesday, Perry took to her Twitter page to post something that sounds like it could easily be referred to the rumored feud with Swift.

"Watch out for the Regina George in sheep's clothing..." she wrote.