Keri Russell and Matthew Rhys play Soviet spies in the FX series "The Americans," but Russell revealed a family secret Friday on NBC's "Today."

The 40-year-old actress was promoting her new movie, "Free State of Jones," when Matt Lauer took a moment to congratulate her on the recent arrival of her baby.

"You just had a baby about a month and a half ago," he said. "Am I correct in reading, Ms. Russell, that you have not yet revealed the gender of the baby or the baby's name?"

She then told Lauer that she and Rhys welcomed a son named Sam.

"He's so good," said the actress, who is also mom to son River, 9, and daughter, Willa, 4, from a previous marriage."[Sam] is big and fat and nice," Russell added.

As for Rhys, a first-time dad, Russell told Lauer he's doing "so well."

Earlier in the interview, Russell discussed director Gary Ross' "Free State of Jones." "It's based on a true, incredible story. It's just this epic, historic film," she said. "I think Matthew McConaughey is great in it."

McConaughey plays a Mississippi farmer who leads an uprising against the Confederacy.

"He's an epic character, and he's not just an altruistic, good guy," Russell said. "He has a lot of flaws and grit."