Naomi Watts Announces She Married Billy Crudup

Naomi Watts is a married woman for the first time in her life -- 'cause she said "I do" to Billy Crudup ... who also walked down the aisle as a newbie.

The actress announced their marriage on social media Saturday, posting a photo of what appears to be her and BC standing on the steps of a courthouse -- where he's in a blue suit and she's in a white dress of some sort ... complete with a bouquet and everything.

Photos of them heading back to their NYC apartment Friday made the rounds ... everyone suspected they might've tied the knot, on account of their matching wedding bands.

Amid all the speculation, NW finally confirmed it ... simply writing, "Hitched!" She's been dating Billy since 2017 -- they met on the set of their shared Netflix show, "Gypsy." Like we said, neither Naomi nor Billy had ever actually been married before this ... although they did each have long-term relationships with other people, which resulted in children, etc.

Billy had been with Mary-Louise Parker and Claire Danes before this. Meanwhile, Naomi was with Liev Schrieber for a long time. Now, at their shared age of 54, they're man and wife.