A nasty fight has erupted between Jamie Lynn Spears and her cheating fiancé, Casey Aldridge.

In the Sept. 15 issue of Star, we reveal that Britney’s little sister, who’s devastated by Casey’s unfaithfulness yet again, is gearing up for the fight of her life — for custody of their 2-month-old daughter Maddie. This latest chapter in the teen couple’s troubled saga could spell major heartache for Jamie Lynn as Star has learned that Casey is ready to gear up for a courtroom brawl to keep Maddie — and the one-time TV star’s money — close at hand.

“He’s not a spiteful person,” a friend of his tells Star. But he feels he’s entitled to a chunk of Jamie Lynn’s millions. “He plays to win. He doesn’t really want full custody of Maddie, but he knows it might be his best weapon against Jamie Lynn.”

But don’t think Jamie Lynn will go down without a fight. Sources say the 17-year-old may talk to her own attorneys and might be willing to cut off Casey’s money supply and sell their house in Liberty, Miss., reveals the insider. “She was giving him tens of thousands of dollars for electronics, video games and the truck that she bought him — in fact, he spent $8,000 last month alone on gas and sporting equipment.”

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