The two singers have been pop rivals ever since Katy allegedly poached three back-up dancers from Taylor's Red World Tour for her own Prism World Tour back in 2013.
Taylor seemingly referenced the feud in an interview in 2014, when she claimed her song Bad Blood was about a "straight-up enemy" who tried to sabotage her trek.
"She did something so horrible. I was like, 'Oh, we're just straight-up enemies'. And it wasn't even about a guy! It had to do with business," Taylor told Rolling Stone magazine at the time. "She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me... So now I have to avoid her. It's awkward, and I don't like it."
Despite Katy refusing to talk about the spat in interviews, she has taken aim at her former friend in thinly-veiled insults on social media.
After Taylor's Rolling Stone interview was published, she took to Twitter and posted, "Watch out for the Regina George in sheep's clothing," a reference to Rachel McAdams' two-faced character in Mean Girls.
The bitter fall out hit headlines again recently after Taylor split from DJ Calvin Harris, who later accused the Shake It Off star of trying to "bury" him like she did to Katy.
Now Katy's parents have waded into the feud, telling Grazia magazine their daughter is trying to rise above Taylor's insults.
"Katy released Rise," her mother Mary began. "It says, 'My feet have been put to the fire but I will rise.' That's what she's about right now."
Her dad Keith added, "You know it ain't over yet (sic)." Calvin made the reference to the Katy/Taylor feud in a series of tweets aimed at his ex after Taylor's representatives confirmed she had secretly written his Rihanna collaboration, This Is What You Came For, and suggested the DJ had been trying to hide her contribution to the song. You may also like: Katy Perry reignites Swift feud "Hurtful to me at this point that her and her team would go so far out of their way to try and make ME look bad at this stage though..." he wrote on Twitter in early July, 2016 before addressing Taylor herself, adding, "I know you're off tour and you need someone new to try and bury like Katy ETC but I'm not that guy, sorry. I won't allow it."
Katy seemingly responded to being dragged into the argument between the former couple by posting a gif of U.S. presidential candidate Hillary Clinton rolling her eyes and shrugging her shoulders.
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