Kevin Costner's Wife, Wealth Increased from $100 Million to $400 Million During Marriage

Kevin Costner's got a ton of money -- that's no secret --  but what's really insane is just how much his wealth expanded during his marriage to Christine Baumgartner, at least according to her.

Christine says in legal docs, obtained by TMZ, back in 2004 when the couple was hammering out their prenup, Kevin disclosed he had $102,716,000 in assets ... but she now says she doesn't know if that was full disclosure.

Fast forward to 2023, as the two are working to finalize their contentious divorce ... Christine says she believes Kevin's worth is close to $400 million ... with about $24 million in cash.

It's wild to think Kevin's grown his wealth 4x in less than 20 years -- obviously, he's been in some big projects -- but it's still super impressive ... if Christine's telling the truth.

As for what he's done in those years ... Kevin starred in "Yellowstone" from 2018 to 2023, acted in movies like "Let Him Go," "Hidden Figures," and "Draft Day."

He's also started the band "Kevin Costner & Modern West" -- they toured and put out 4 albums -- and he co-authored "The Explorer's Guild: A Passage to Shambhala."

So nothing THAT crazy, but Costner clearly gets good financial advice and has an impressive real estate portfolio ... including a beachfront estate as well as a separate plot of land worth a reported $145 million.

BTW ... he's also been involved in the oil industry.