Kevin Costner‘s divorce was as ugly as they come — and much of it had to do with claims of infidelity on both sides … something denied by all sides and featured in a new ‘360aprokoInvestigates.’

The A-lister’s split from his wife, Christine Baumgartner, kickstarted with unfounded rumors of KC impregnating someone on the set of “Yellowstone” — something we dive into in detail in a new documentary airing Monday on FOX, ‘Kevin Costner’s Divorce War.’

Now, when it comes to CB herself — there were rumblings of alleged cheating as well … on two different fronts, actually. There was a guy who was staying in their guest house — whom she was alleged to have slept with — he shut that down, saying it never happened.

There was also Josh Connor … a friend of Kevin and Christine who — as soon as they were in the midst of divorce — started to hang out a lot with Christine on vacations. Again, sources connected to both of them say there was absolutely nothing romantic going on before or during the divorce.

“360aproko Investigates: Kevin Costner’s Divorce War” airs Monday at 9/8c on Fox and starts streaming the next day on Hulu.