Last year, Mel Gibson's ex turned down a settlement that would have gotten her $15 million in support payments from the actor.

Not enough, Oksana Grigorieva -- with whom Gibson has a daughter -- concluded.

She's regretting that moment this morning.

Yesterday, an L.A. County judge ruled that Gibson owes Grigorieva just $750,000.

He'll also continue to help pay for the home in which Grigorieva and the child live.

But wow, that's a lot of dough to leave on the table.

And perhaps the even better deal for Gibson out of this ruling is that the judge was clear: both of them, from here on out, have to keep their mouth shut about their bitter breakup.