Source tell Star that Kevin is seriously unhappy with the 50-50 custody division of time with their sons, Sean Preston, 22 months, and Jayden James,10 months. He is legally free to fight the ruling – and insiders insist he’s intent on doing so ASAP! “Kevin is absolutely dead set on getting full custody of his sons,�? a friend of Kevin tells Star. “I’m positive he’ll be going back to court!�?

This time, Kevin may finally win full custody, thanks to a potent secret weapon: The pop star’s former personal assistant, Shannon Funk, who could tip the scales in Kevin’s favor by detailing Britney’s bizarre behind-the-scenes antics!

Funk had been working as Brit’s assistant for just 3 weeks when strange reports surfaced that Britney fired her in late July because she suspected her of disloyalty. According to these reports, Funk was threatening to write a tell-all about Brit’s wild partying, questionable mothering skills and bizarre behavior. But when Star spoke with Shannon, she denied that she’d been fired or was planning to pen a tell-all. “I’m still Britney’s assistant,�? she told Star.

However, says an insider, “Shannon contacted Kevin’s friends at one point – and that gave him the idea that she might rat Brit out. Then Kevin contacted Shannon. She told him she had cell phone pictures of Britney and herself partying – including pictures of Britney acting silly while intoxicated and running around the house barely clothed!�?

That’s why Kevin determined to have Funk testify against Brit when he reopens the case! “He thinks it’s better to have Shannon tell the court about Britney than just say it himself,�? the insider adds.