'Unconscionable:' Kevin Costner's Estranged Wife's Secret Plan to Contest Prenup in $400 Million Divorce War Revealed

Kevin Costner’s estranged wife has finally revealed the plan to legally squirm out of the ironclad prenup — and only RadarOnline.com can exclusively expose the secret divorce court maneuver to cash in on the megastar’s $400 million fortune.

The legal strategy was discreetly inserted in court documents seeking to compel the Dances With Wolves star to fork over ALL of his financial records in preparation for an evidentiary hearing in late August.

For months, Christine Baumgartner and her legal team have refused to explain why or how they plan to challenge the premarital agreement (PMA) she signed weeks before their 2004 wedding.

As RadarOnline.com previously reported, the PMA required the Hidden Figures actor to pay his ex $1 million after she filed for divorce in May, plus $200k for moving expenses and $30k a month in child support for their three children, ages 16, 14, and 13.

But the savvy Baumgartner, 49, refused to vacate his prized $145 million estate in Carpinteria, California, within 30 days as prescribed by the PMA until she was paid $232k a month in child support – pending the battle over the validity of the prenup later this year.

Santa Barbara Superior Court Judge Thomas P. Anderle ended the skirmish last month when he ordered the handbag designer to vacate the massive spread by July 31 — and forced the Tin Cup star to temporarily pay $129k a month in support.

Costner’s legal team later accused Baumgartner of “gamesmanship” when she refused to explain why she was contesting the prenup, according to court documents seeking to impose a $14,237.50 fine on her for stalling the legal proceedings.

“Kevin has been prejudiced by Christine’s dilatory conduct, evasive responses and continuing refusal to make all of her contentions known,” Costner powerhouse lawyer Laura Wasser wrote in a scathing motion seeking to sanction Baumgartner.

Baumgartner returned the favor and accused her husband of being “evasive” by refusing to provide financial records for every penny he’s earned over the past couple of years – including top secret contracts for his hit TV series Yellowstone and his massive four-film series Horizon: An American Saga.

Incredibly, the Field of Dreams actor has already turned over about 10,000 pages of financial records, but Baumgartner’s team of bloodhound forensic accountants charge they are still missing copious amounts of documents and statements. Baumgartner wants Costner slapped with a $8,985 fine.

The financial scrum kicked off on June 2 when their respective lawyers and forensic accountants began bickering over what financial records were relevant in the divorce drama, the court documents showed.

Costner’s lawyers argued they have provided documents for 98 percent of his cash flow available for support payments – since the terms of the prenup make all the other financial evidence irrelevant.

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But Baumgartner wants all the financial documents in preparation for the trial contesting the PMA and possibly charging she was unwittingly short-changed in the deal.

“As you are aware, one part of the analysis as to whether the Agreement (or parts thereof) are unconscionable is to compare the terms of the Agreement against the parties' financial realities,” Baumgartner’s lawyer wrote in an August 1st letter to Costner’s lawyer.

“To do so, (Baumgartner) is entitled to financial discovery on your client, including his separate property.”

The bare-knuckle divorce brawl kicked off in May when Baumgartner blindsided the 68-year-old Oscar-winning actor with divorce papers after 18 years of marriage.