Christine Baumgartner beat Kevin Costner to the courtroom.

When the handbag designer filed for divorce in May after 18 years of marriage, the actor was reportedly “blindsided” as he had planned to file first.

The “Yellowstone” alum’s “lawyer was getting the paperwork drawn up” when his estranged wife “sneak attack[ed] him and serve[d] him with her own set of divorce papers,” a source told the US Sun over the weekend.

“Kevin was so shocked,” the insider added on Sunday, alleging that “Christine has since made him look terrible and has continued to do so.”

However, a longtime friend told Page Six last month that Costner was “stunned by Christine’s actions” because he didn’t “want the divorce, and he would take her back.”

Page Six has reached out to Costner’s rep for comment.

The Golden Globe winner and Baumgartner, 49, got married in 2004 and share three kids — Cayden, 16, Hayes, 14, and Grace, 13.

Costner filed for joint custody of the little ones last month in response to Baumgartner’s divorce filing.

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The duo’s divorce proceedings have since grown contentious, with Costner claiming his partner has refused to move out of their California home and charged $95,000 on his credit card amid their breakup.

The Cat Bag Couture creator, for her part, accused the Oscar winner of telling their kids about their split via a 10-minute Zoom call.

“He insisted that he had the right to tell them that we were getting divorced ‘first’ and tell them privately ‘without me present,” she alleged in court documents obtained by People.

Baumgartner, who is requesting nearly $250,000 in monthly child support payments, also called out Costner’s allegedly extravagant spending earlier this month, from $830,000 for gifts to $449,000 for beach club fees.

The financial revelations came after Costner told the courts he wanted his bank records kept private due to “unwanted and embarrassing global media attention,” as well as “irreparable” harm by burglars.