Wowsers. We probably didn't need confirmation that you just don't mess with Taylor Swift – but if we did, that's now happened.
And it's happened in SPECTACULAR fashion. Here's the back-story:
Earlier this evening, former One Directioner Zayn Malik shared a now deleted tweet from the @FemaleTexts account with his 15.4m followers.
The message (ouch) negatively compares one Taylor Swift to fellow pop star, Miley Cyrus, and includes a screenshot of an interview with TIME.
In the interview, Ms Swift encourages her fans to download her music from iTunes now that she's withdrawn from Spotify.
In contrast, Ms Cyrus's quote explains that as she's already “made [her] money” she doesn’t care if “no one buys [her] album.” Then there's a description of Cyrus’s Happy Hippie Foundation, which benefits LGBT youth.
The tweet concludes: “The difference is astounding.”
Right or wrong, the sentiment is clear: multi-millionaire Taylor Swift, 25, is intent on making LOTS more money for herself – while Miley Cyrus, 22, is more concerned with using her celebrity and fortune to help others.
Understandably, it is an accusation that Tay-Tay's boyfriend wasn't about to take lying down.
"You've made your money?" he began addressing Mr Malik via the social-networking site. "Cool… fuck the 99% of musicians who depend on these services to survive right? Yeah fuck em."
A series of tweets ensued, including the line: "There's some poor fucker in a basement making your new favorite record trying to survive."
Zayn then fought back: "Ha you just made an absolute fool of yourself mate," he began, adding: "I suggest you calm your knickers before them dentures fall out."
The 22-year-old concluded with: "Oh and I write my own shit too dickhead."
Taylor herself has yet to get involved – although 31-year-old Calvin did appear to offer an olive branch of sorts to his rival in the end.
For now, Mr Malik has bowed out of the contest: he's giving the Scottish DJ the silent treatment.
Whatever next… Perrie Edwards throwing in her tuppence worth? Well, Little Mix did just appear on stage with Taylor in California.
Yup, it seems lines have been drawn.