Keri Russell is reportedly pregnant.

Keri Russell

Keri Russell

The 39-year-old star - who already has son River, eight, and daughter Willa, four, with ex-husband Shane Deary - and her 'Americans' co-star Matthew Rhys are expecting their first child together and the actress is said to already be in her second trimester.

A source said: "Keri is more than four months along."

Another source added: "It's so exciting for them!"

The couple were rumoured to be dating for some time but deflected questions about any romance until they finally made their first public appearance as a couple in April 2014.

And the 41-year-old actor couldn't be more smitten with Keri.

A source told Us Weekly magazine: "They are always together and love roaming around New York.

"Matthew is really in love. They feel they should have always been together."

Representatives for both Keri and Matthew have not commented on the news.

Keri previously said she enjoyed the "freedom" of her role in the spy drama, in which she and Matthew play KGB agents posing as a married American couple.

She previously said: "It's not this big sweeping romantic movie where you have to be so in love and so beautiful and so sexy.

"You're usually using the sexuality, at least in the spy end of it, to get something.

"So there is kind of a freedom in that, because it's kind of messier or more direct than that."