Divorce War Looms as Kevin Costner Said to be ‘Concerned’ Estranged Wife Will Challenge Prenup in $250 Million Divorce: Sources

Kevin Costner's fears have grown that his estranged wife, Christine Baumgartner, will fight against the prenuptial agreement they have in place after she filed for divorce to end their 18-year marriage, RadarOnline.com can exclusively report.

We're told Costner is "concerned" that "Christine is making moves to challenge the prenup," a source close to the situation claimed.

Baumgartner cited "irreconcilable differences" as the reason behind their split after months of speculation there had been trouble in paradise while he was busy filming the Western mega-hit Yellowstone. Both exes are currently seeking joint custody of their three minor children.

In his filing, Costner made mention of a prenup which determined how they would allocate spousal support, legal fees, and properties in the case of a breakup.

"Miscellaneous jewelry and other personal effects; earnings and accumulations of Respondent before marriage, during marriage, and from and after the date of separation; [and] there are additional separate property assets and obligations of each party as mandated by the parties' Premarital Agreement," Costner's legal team wrote.

The filing also stated that Baumgartner needed to leave his homes, reading, "Pursuant to the terms in Paragraph 9.A. of the parties' Premarital Agreement, Petitioner to vacate Respondent's separate property residences."

Costner will be adjusting to two big life changes at once as it was confirmed he will be leaving Yellowstone after season 5. As we previously reported, "ditching Yellowstone was part of Kevin's desperate attempt to save the marriage," a previous insider spilled.

Prior to Baumgartner, Costner was last married to Cindy Silva, tying the knot in 1978. Their 1994 divorce resulted in an estimated $80 million settlement to his ex.

Years after their split, Silva and Coster "are very good friends now," a tipster told RadarOnline.com in an update.

Never miss a story — sign up for the RadarOnline.com newsletter to get your daily dose of dope. Daily. Breaking. Celebrity news. All free.

As for his anticipated court battle, the source said that he shouldn't be too worried no matter what the outcome is. "Kevin's prenup is airtight," the tipster claimed. "Christine will just be causing nothing but grief and more drama."

RadarOnline.com has reached out to a Costner rep for comment.