According to TMZ, Justin was "working out" (read: goofing around and dancing to his new track "Yummy" in front of a wall of mirrors) at Dogpound Gym in Los Angeles' West Hollywood neighborhood recently when Taylor and her entourage arrived.
Sources tell the website Taylor's bodyguards asked everyone in the gym, including the singer's nemesis and best friend's ex, Justin, was asked to leave because Taylor had a solo appointment with a trainer.
Although they hadn't been told specifically that it was Taylor who was booting them out, Justin and his security team reportedly announced they weren't going anywhere until Justin was done working out.
The website notes it's not clear why Justin wasn't given a warning he'd have to leave before Taylor's security team arrived. Justin did clear out, though, along with everyone else.
The pop stars have a history of bad blood that was exacerbated over the summer when Justin's longtime manager Scooter Braun bought the Big Machine Records label, thereby gaining ownership of Taylor's entire back catalog.
Taylor responded by posting an open letter on Tumblr in which she detailed the ways Scooter, often with Justin's help, had "bullied" her over the course of her career.
"For years I asked, pleaded for a chance to own my work. Instead I was given an opportunity to sign back up to Big Machine Records and 'earn' one album back at a time, one for every new one I turned in," she wrote in June. "I walked away because I knew once I signed that contract, Scott Borchetta would sell the label, thereby selling me and my future. I had to make the excruciating choice to leave behind my past. Music I wrote on my bedroom floor and videos I dreamed up and paid for from the money I earned playing in bars, then clubs, then arenas, then stadiums."
She went on to say that when she learned Scooter had bought her masters, "…all I could think about was the incessant, manipulative bullying I've received at his hands for years." She then recounted being bullied by Scooter and Justin online about the phone call between Taylor and Kanye West that Kim Kardashian West recorded, allegedly illegally, and leaked.
"Or when his client, Kanye West, organized a revenge porn music video which strips my body naked," she continued. "Now Scooter has stripped me of my life's work, that I wasn't given an opportunity to buy."
The not-so-happy ending of Justin's long-term romance with Taylor's close friend Selena Gomez only fueled tensions between the two.