Kevin Costner is facing a nightmare $100 million bill after his vanity project, the Western movie saga Horizon, flopped at the box office,

according to insiders who say he’s being forced to cash in a trove of precious assets to pay the massive debt.

As RadarOnline.com previously reported, the Yellowstone star, 69, mortgaged his stunning 10-acre Santa Barbara ranch to help fund

the ambitious four-part big-screen epic.

Part one only brought in $11 million on opening weekend, and part two has been pulled from its original August release. Now, sources claimed he would have to cough up some serious money.

kevin costner shuts down gayle king interview yellowstone departure

Source: MEGACostner announced he was leaving ‘Yellowstone’ as ‘Horizon’ bombed at the box office.

The insider said: “Kevin banked Horizon largely on undeveloped California land he owns.

“Now reality is starting to set in that he’s likely going to have to part with this real estate and reshuffle his other holdings to remain solvent after the disappointing first film showing.”

Adding to his financial woes, Costner’s recent divorce from Christine Baumgartner, 50, his wife of 18 years and mom of three of his kids, cost him a huge chunk of his estimated $400million fortune.

Composite photo Kevin Costner Christine Baumgartner

Source: MEGACostner and Christine Baumgartner’s split played out in the media.

The insider continued: “His divorce wasn’t cheap.

“He’s paying Christine $63,000 in child support and he still gives his kids a lot more money on top of that.

“But this film investment is the real killer. It’s been a giant piano hanging over his head.”

Kevin Costner and Taylor Sheridan

Source: MEGACostner (right) and the show’s creator Taylor Sheridan (left) reportedly came to blows over the show’s filming schedule.Online TV streaming services

Costner, who admittedly is “not a very good businessman”, insisted on putting his own money into his passion project and is determined to get the series out.

The insider added: “There’s still some momentum behind these films, even if it’s all coming from Kevin.

“But it’s becoming clearer he probably should have made this a TV miniseries, and then he never would have gotten into this hole.”

Instead, Kevin is reorganizing his life, his finances and his possessions around funding Horizon for a couple more years.

“He’s operating on a wing and a prayer, but he’s also a realist who knows he’s going to have to part with some of his treasure to see this thing through to the end.”

kevin costner sparks skin cancer fears top doctor warns

Source: MEGAKevin Costner posed with the cast of “Yellowstone” at the season 1 premiere.

Costner also walked away from his massive Yellowstone paycheck this year.

Citing scheduling conflicts and a rumored feud with creator Taylor Sheridan, 54, he announced he would not return for the second half of Season 5 earlier this year.

Costner’s decision cost him not only his $1.3million per episode paycheck but also his relationships with the once-close cast.

“Other than Kelly, who had fame for the Sherlock Holmes movies, Kevin made most of these people the big stars they are.”

The source added: “Even Kelly’s star rose higher because she and Kevin played off each other so well.”