"Taylor got upset over something crazy and then she just alienated Karlie," a source told Page Six on Saturday, Aug. 10.
Rumors recently surfaced that Karlie invited a bunch of friends over to Taylor's $47.7 million Tribeca pad, where she allegedly even had her own bedroom. But Taylor was reportedly pissed that she took advantage of her generosity and didn't ask permission before bringing in her bevy of guests.
Reps for both stars have denied that the miscommunication was the exact straw that broke the camel's back, but the source claims their beef began over a tiff that got way out of hand.
Another insider added, "She always does the same thing: she trips up when she goes further than she needed to."
The former BFFs haven't been spotted together since Karlie attended one of Taylor's Reputation Tour concert dates in Nashville exactly a year ago.
"No one puts on a show like @taylorswift 🎤✨," Karlie captioned a pic with the "You Need to Calm Down" songstress on Instagram. "Nashville was out of this world, I am SO proud of you."
Taylor also reportedly turned down invitations to Karlie's two wedding ceremonies to Josh Kushner in October of last year.
Adding insult to injury, Karlie's modeling career is managed by Scooter Braun, who Taylor recently had an explosive public fight with over his newly purchased rights to her old music catalog.
Taylor called Scooter a "manipulative bully" after he signed a $300 million deal with her former label, Big Machine, in June.
But Karlie has become super-close with the music mogul despite his business drama with Taylor. In fact, she and her husband just vacationed with Scooter and his wife, Yael, in the Mediterranean.
"Week of laughter," Scooter captioned a group photo aboard a yacht with Karlie on Instagram on Aug. 10.
Taylor, who's been privately dating "The Favourite" actor Joe Alwyn since 2016, is keeping busy enough without Karlie these days. Her seventh studio album, "Lover," is set for release on Aug. 23.