Sebastian Stan and Girlfriend Annabelle Wallis Welcome First Baby Together

Sebastian Stan and girlfriend Annabelle Wallis have officially welcomed their first baby together!!!

Sources with direct knowledge tell us the couple has officially become a family of three, and we're told the newborn arrived last month.

We broke the story that the two actors -- who have been together for about four years -- have been gearing up to welcome a baby, though details like the due date and gender of the child were under wraps at the time.

The timing comes during a particularly busy stretch for both stars ... Sebastian has a packed year ahead with the upcoming release of his film “Fjord” ... along with the highly anticipated Marvel installment “Avengers: Doomsday.”

Annabelle has a couple of big projects on the horizon as well. She stars alongside Jason Statham in the action film “Mutiny” -- slated to hit theaters in August -- and she’s also set to appear in Netflix’s “Unabomb,” a project about the Unabomber, Ted Kaczynski.