Seal and Heidi Klum

HEIDI KLUM's divorce from SEAL is erupting into an ugly battle as the "Kiss From a Rose" singer prepares to go after a huge chunk of her $70 million fortune, say sources.

The 38-year-old supermodel filed for divorce April 6, stating they have a post-nuptial agreement, which means they agreed to keep their assets completely separate during their marriage.

But Seal has struck back, filing his own documents that make no mention of their post-nup, yet note that California is a community property state — which could entitle him to half of the beauty's megabucks.

"Even though they may have had a post-nuptial agreement, it appears that Seal is going to challenge it," said a legal strategist. "If he is successful, it could mean big bucks for him in their divorce.

"Seal could go after half of everything his wife earned during the marriage.

"He could also own a piece of her career for years to come since any contract she signed while they were together would be considered community property."

To complicate matters, in december 2010, Heidi and Seal bought a $13.4 million house in Brentwood, Calif. under community property rules, Seal would be entitled to half its value if he successfully challenges the post-nuptial agreement.

"It would be a rare post-nuptial agreement if it didn't cover the things Seal is talking about, but anything is possible," famed divorce attorney Raoul Felder told The ENQUIRER. "There are open issues and, yes, Seal could go after half."

On Jan. 22, Seal and Klum made the shocking announcement that they were separating after nearly seven years of marriage. The singer, whose career has slipped, is worth an estimated $15 million.

Adding more fuel to the fire, the "Project Runway" producer and host is asking for sole physical custody of their four children — ages 2 to 7 — while Seal, 49, is asking for joint physical custody.

A source told The ENQUIRER: "Seal is hurting and I believe he's going to try to make his wife pay for his hurt — to the tune of $35 million."