The "Selling Sunset" star's estranged hubby Christian Dumontet just filed to divorce his wife -- and it looks like he might've gotten ahead of her own filing ... as we know Christine herself has been mulling pulling the plug as well.

According to the docs, obtained by TMZ, Christian is citing irreconcilable differences as the reason he's filing ... and he's also asking for sole legal and physical custody of their son.

He does signal he's open to Christine getting visitation rights to see their boy.

On the issue of spousal support, Christian isn't asking for any alimony -- but he does want the court to terminate Christine's ability to seek spousal support from him. There doesn't appear to be any explicit mention of a prenup.

Christian wants the court to help them figure out what's his and what's Christine's in terms of assets and property -- and he's asking that anything he's made while they've been separated be seen as his own stuff. He lists the date of separation as TBD ... to be determined.

Of course, we all saw this coming ... especially considering how tumultuous things have been between Christian and Christine of late. Remember, he was arrested a few weeks ago for assault with a deadly weapon ... with CQ claiming he'd thrown a bag with glass in it at her, but missed and hit their kid during a big fight they had at their house.

Christian has denied that ... and also sought a restraining order against Christine -- alleging that a big source of their problems was her un-trained dogs. Christine also filed for a restraining order ... making lots of allegations against Christian.

His order was denied, and her order was partially granted ... pending a future hearing. One other interesting thing ... Christian says they got hitched in 2021, not 2019 like everyone thought.