Kourtney Kardashian and Scott Disick are reportedly preparing for what may be a messy permanent split.

Although the couple parted ways nearly one year ago, they are just now making plans to split their assets and establish a custody agreement for their three children, Mason, 6, Penelope, 3, and Reign, 1.

“Scott’s been dating a string of young beauties, while Kourt’s been secretly hooking up with Justin Bieber, and they both know there’s no going back,” a source explained to Radar Online on Wednesday.

Since splitting last summer, Kardashian has been linked on and off to Bieber while Disick has been spotted with a number of models, including Megan Irwin and Christine Burke.

“It’s going to get nasty," the source continued. "Legally, she has Scott over a barrel thanks to his wayward behavior over the years — but Scott is more than willing to play dirty."

As for the current status of Kardashian's relationship with Bieber, they were believed to have parted ways after Kardashian was caught at his hotel, but according to a source, they may be back on and sneaking around in secret.

“Justin’s learned to keep his mouth shut, because Kourtney made it clear she needs this to be discreet for the sake of her kids as well as the complicated situation that’s going on with Scott [Disick],” an insider revealed Radar Online in March.

“That suits Biebs just fine,” continued the insider. “He says Kourtney’s the best lover he’s ever had and he can’t stay away from her... He loves having an older, experienced lover and they have a great friendship connection, too, so it works for both of them.”

As for Bieber's other rumored flame, Hailey Baldwin, the source claimed he was only stringing her along.

For more of Kourtney Kardashian and Scott Disick, tune into Keeping Up With the Kardashians season 12 on Sunday nights at 9 p.m. on the E! Network.

Tags: kourtney kardashian Justin Bieber scott disick