Taylor says she's been unable to own the rights to her own music because of a record deal she signed at 15
Taylor Swift has accused Scooter Braun, who manages Justin Bieber and Kanye West, of bullying after he became the owner of most of her music.
He's bought record label Big Machine for $300 million (£237m), which means he owns the masters to her six albums.
So he now makes money from every song Taylor released before this year's Me! with Brendon Urie.
Taylor says she's been unable to own the rights to her own music because of a record deal she signed at 15.
She wrote on Tumblr about her attempts to take back the rights to the music she's released on Big Machine, and her feeling that Scooter has attempted to "dismantle" her legacy.
A lot of people are now involved - here's what's happened and who's said what so far.
What Taylor says
"For years I asked, pleaded for a chance to own my work," she wrote.
Taylor claims Big Machine offered her a chance to earn "one album back at a time" in exchange for every new one she recorded after her original record contract with them expired.
But she's now signed to Universal's Republic Records label, and says signing a new deal with Big Machine would have been used to help encourage the sale of the company.
"I had to make the excruciating choice to leave behind my past," she says.
"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."
Big Machine still owns the rights to the six albums she released between 2006 and 2017, and she says she only learned about Scooter Braun taking over the label when it was announced.
"All I could think about was the incessant, manipulative bullying I've received at his hands for years."
Taylor was referring to the Kanye West song Famous, which includes lyrics about wanting to have sex with Taylor and features a naked replica of her in the video.
Kim Kardashian shared some of a phonecall between Kanye and Taylor on Snapchat at the time, saying it showed Taylor had been spoken to about the song before its release.
Taylor denied the conversation took place.
"Now Scooter has stripped me of my life's work, that I wasn't given an opportunity to buy. Essentially, my musical legacy is about to lie in the hands of someone who tried to dismantle it," she continued.
"This is my worst case scenario. This is what happens when you sign a deal at 15," she wrote.
"Never in my worst nightmares did I imagine the buyer would be Scooter. Any time [Big Machine founder] Scott Borchetta has heard the words 'Scooter Braun' escape my lips, it was when I was either crying or trying not to.
"He knew what he was doing; they both did. Controlling a woman who didn't want to be associated with them."
What Justin Bieber says
In her Tumblr post Taylor also shared a photo posted by Justin Bieber shortly after the leaked phone call.
It showed Justin on a video call with Scooter Braun and Kanye West, with the caption "Taylor Swift what up" (which has since been deleted), calling it an example of the bullying she faced.
Justin Bieber has since responded, apologising to her for the 2016 picture and saying it was "distasteful and unfair" - but also criticising her comments about Scooter Braun.
"For you to take it to social media and get people to hate on scooter isn't fair," he wrote.
"What were you trying to accomplish by posting that blog? Seems to me like it was to get sympathy. You also knew that in posting that your fans would go and bully Scooter."
What Big Machine say
Meanwhile, Scott Borchetta has posted an open letter on the Big Machine website offering his side of the story.
He claims he personally contacted Taylor to tell her about the sale on 29 June, says he "never experienced" her in tears over Scooter Braun and says that she was given an opportunity to take control of her masters.
"Taylor had every chance in the world to own not just her master recordings, but every video, photograph, everything associated to her career," he says.
"She chose to leave."
Who else is involved?
Demi Lovato, who's also managed by Scooter, posted support for him on her Instagram story.
Todrick Hall, Taylor Swift's friend who executive produced her new video You Need To Calm Down, said he believes Scooter Braun is "evil".
Scooter Braun's wife, Yael Cohen Braun, shared a note on Twitter claiming that Scooter had said he was "excited" to work with Taylor through his ownership of Big Machine.
And Model Cara Delevingne responded to Justin Bieber's post on Instagram, saying she's not sure he understands "what an apology is".
"I wish you spent less time sticking up for men and more time trying to understand women and respecting their valid reactions," Cara wrote.
Newsbeat has contacted Scooter Braun for comment, but he is yet to respond.