Cue the mudslinging.

Just a few weeks after publicly making amends with long-time frenemy Katy Perry, Taylor Swift sparked a new brouhaha with a major music industry heavyweight – triggering backlash (and backup) from some of the world’s biggest popstars.

In less than 24 hours, the fight has dredged up Swift’s longstanding rift with Kanye West and Kim Kardashian, earned a half-apology from Justin Bieber and prompted accusations of lies, deleted Instagram posts and even homophobia.

In short, the situation is messy. Here’s what you need to know.

WHAT HAPPENED?

It all began with a Tumblr post.

On Sunday, Swift published a 449-word takedown that accuses music manager Scooter Braun, who is best known for managing Justin Bieber, of years of “incessant, manipulative bullying.”

Swift’s post came on the same day that news broke that Braun purchased the original recordings of Swift’s songs, otherwise known as masters.

According to Swift, she was never given the opportunity to buy the masters herself, and now they’re in the hands of someone she alleges tried to ruin her career.

“Like when Kim Kardashian orchestrated an illegally recorded snippet of a phone call to be leaked and then Scooter got his two clients together to bully me online about it,” Swift wrote.

In her post, Swift attached one of Bieber’s old Instagram pictures, which also depicts Braun, with the caption “Taylor swift what up.”

Bieber made the jibing post in 2016 after Kim Kardashian released an audio recording of a telephone conversation between her husband, Kanye West, and Swift, that appeared to show Swift approving unflattering lyrics about Swift in West’s song “Famous.” (Swift had previously denied giving West permission to call her a “bitch” on the track.)

Swift also linked Braun to West’s video for “Famous,” which she described as “a revenge porn music video which strips my body naked.” West is one of Braun’s clients.

“Now Scooter has stripped me of my life’s work, that I wasn’t given an opportunity to buy,” Swift wrote.

But Braun wasn’t the only one implicated in the post. Swift also called out Scott Borchetta, CEO of Big Machine Records, who scouted out Swift when she was a teenager.

In her post, Swift accused Borchetta of selling her out.

“This is what happens when you sign a deal at fifteen to someone for whom the term ‘loyalty’ is clearly just a contractual concept. And when that man says ‘Music has value’, he means its value is beholden to men who had no part in creating it,” she wrote.

“When I left my masters in Scott’s hands, I made peace with the fact that eventually he would sell them. Never in my worst nightmares did I imagine the buyer would be Scooter. Any time 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. In perpetuity. That means forever.”

Swift, who has since signed with Universal Music, ended the post by saying that she is still proud her of earlier music, but that she feels “sad and grossed out” by the debacle.

She also plugged her new album, “Lover,” which she pointed out is due for release on August 23.

THE FALLOUT

It didn’t take long for the pile-on to begin.

Bieber quickly responded with an Instagram post that begins as an apology before accusing Swift of playing the victim.

Bieber said Braun didn’t have anything to do with the “Taylor swift what up post” and that he actually discouraged him from posting it. He also accuses Swift of “crossing a line” by publishing her grievances on the internet.

“What were you trying to accomplish by posting that blog? Seems to me like it was to get sympathy u also knew that in posting that your fans would go and bully scooter,” he wrote.

Bieber added that he’s open to talk with Swift about the situation: “Anyway, one thing I know is both scooter and I love you.”

Braun’s wife, Yael Cohen Braun, was less diplomatic. She accused Swift of flat-out lying about not having a chance to buy her own masters.

“You were given the opportunity to own your masters, you passed,” she wrote on Instagram. “Your dad is a shareholder and was notified, and Borchetta personally told you before this came out.”

Borchetta stood by the same version of events. In a statement, Borchetta said Swift’s father was alerted to the masters deal before it went through. He added that he texted Swift on Saturday to let her know about Braun’s purchase.

“Taylor has every chance in the world to own not just her master recordings, but every video, photograph, everything associated to her career. She chose to leave,” Borchetta wrote.

Braun’s wife also poked fun at Swift’s accusation of bullying, and suggests that Swift is the real culprit.

“The world has watched you collect and drop friends like wilted flowers,” she wrote.

Demi Lovato also jumped in to support Braun. In an Instagram story posted late Sunday, Lovato described the manager as a “good man” and told critics to lay off.

“Y’all can come after me all you want but I’m always gonna stay loyal to my team,” she wrote.

TEAM TAYLOR

Swift has plenty of supporters in her corner.

Model Cara Delevingne, a longtime friend of Swift, responded to Bieber’s Instagram post by encouraging him to “take a step back and try to learn from this.”

“I wish you spent less time sticking up for men and more time trying to understand women and respecting their valid reactions,” she wrote.

The comment has since been deleted from Bieber’s post.

Singer Todrick Hall, who served as co-executive producer on Swift’s latest music video “You Need to Calm Down,” blasted Braun on Twitter and accused him of being a homophobe.

“He is an evil person who’s only concern is his wealth and feeding his disgusting ego. I believe he is homophobic & know from his own mouth that he is not a Swift fan,” Hall wrote.

“I truly hope justice is served and that my friend’s music will fall into the hands of a better human.”

Demi Lovato responded to Hall’s comments and defended Braun, insisting that he isn’t homophobic.

“Please don’t spread information that isn’t true because I can guarantee you Scooter isn’t. As a member of the LGBTQ+ community myself, he wouldn’t have signed me if he was,” Lovato wrote.

Pop star Halsey also stood by Swift, saying the situation depicts a larger problem of how writers are treated by the music industry.

“She deserves to own the painstaking labor of her heart,” Halsey wrote on Twitter.

SOME CONTEXT

The spat comes one month before Swift is set to drop her new album, and the popstar has been known for harnessing controversy to sell records.

Swift’s last album, “Reputation,” launched with the single “Look What You Made Me Do,” which many critics saw as a lyrical tongue-and-cheek rebuke to Kanye West and Kim Kardashian.

Similarly, her 2015 single “Bad Blood,” about the betrayal of a close friend, was widely believed to be about Katy Perry, with whom Swift has had an on-again, off-again friendship. The pair recently made amends after Perry appeared in Swift's new music video.