Taylor Swift describes 'worst nightmare', Justin Bieber says she's 'crossing a line'

Justin Bieber has called out Taylor Swift for a lengthy blog post in which she describes music mogul Scooter Braun buying her music as something she'd never imagine in her "worst nightmares".

On Tumblr the 'Bad Blood' hit-maker told fans that Braun's purchasing of her masters made her "sad and grossed out", accusing him of "incessant, manipulative bullying" over her career.

Swift referenced Braun - who discovered and went on to manage Justin Bieber - as being involved in her feud with Kanye West and Kim Kardashian over the notorious 'Famous' lyrics: "I think me and Taylor might still have sex/I made that bitch famous".

"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," she wrote.

"Or when his client, Kanye West, organised a revenge porn music video which strips my body naked.

"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."

Swift called the situation her "worst case scenario", but hoped that aspiring young musicians would read her post and proceed with caution when signing record deals, as she did at the age of 15.

In response, Bieber posted an open letter to Swift in which he apologises to her, tells her he loves her, but ultimately says her post was "crossing a line".

"First of all I would like to apologise for posting that hurtful Instagram post," he said.

The post in question was uploaded by Bieber at the time of the 'Famous' feud, and showed him FaceTiming with West and Braun, who were seemingly making fun of Swift.

"At the time I thought it was funny but looking back it was distasteful and insensitive," he continued.

"Scooter has had your back since the days you graciously let me open up for you!

"As the years have passed we haven't crossed paths and gotten to communicate our differences, hurts or frustrations. So for you to take it to social media and get people to hate on Scooter isn't fair.

"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 [sic].

"Anyway, one thing i know is both Scooter and I love you. I feel like the only way to resolve conflict is through communication."

Bieber concluded that both he and Braun would "love to talk" to Swift about the issue.

"I usually don't rebuttal things like this but when you try and deface someone I loves character thats crossing a line [sic]," he finished.

Swift hasn't publicly responded to Bieber's message, but did retweet a note from fellow singer Halsey, who came out in support of Swift sharing her story.