The Americans actress is pregnant with her third child, a source confirms to PEOPLE.
“They’re thrilled,” a friend of the couple tells PEOPLE.
Already mom to daughter Willa Lou, 3, and son River, 7½, this will be Russell’s first child with her Americans costar.
After months of relationship rumors — and several sightings of the two together — PEOPLE confirmed in April 2014 that Russell and Rhys, 41, were an item.
The former Felicity star, 39, has been honest about the hardships that come with balancing a family along with a successful career.
“I like working hard, but my life outside of my career is equally important to me,” she told PARADE. “Maybe I’m not ambitious enough, but I’m just as interested in my friends and my relationship with my family.”
But becoming a mother has changed Russell for the better. “You instantly become less selfish. You can’t be the biggest person in the world anymore — they are. It really grounds you,” she said.
— Anya Leon with reporting by Elizabeth Leonard and Julie Jordan