The divorce between "Game of Thrones" director Alex Graves and his estranged wife has gone nuclear ... he claims she's a vindictive, unbalanced woman who's holding their kids hostage.
Graves claims in court docs -- obtained by TMZ -- that his wife Sarah refuses to let him see his 15-year-old son and 11-year-old daughter unless he falls for her ploy to get more money.
Graves says he worked his ass off as a Hollywood director to provide a stable, upscale lifestyle for his family ... with exotic trips and festive holiday celebrations.
But Graves thinks his wife resented his work and complained for years he didn't earn enough because he's too stupid.
He says she's bipolar and is fixated on the belief he's having an affair. Graves accuses Sarah of spying on him and using their son to try to bait him into admitting infidelity.
We've contacted Sarah's attorney ... so far no word back.