It has been rumoured for several weeks that the actress is expecting a baby with Rhys.
And now Emmerich, who stars with the pair in hit television show "The Americans", has revealed the happy news is true, reported Entertainment Tonight.
Emmerich said that Russell's pregnancy will not be written into the show.
"First of all, Keri's really petite. It looks like she swallowed a large pea. But yes, we shoot around it.
"She's always standing behind a huge counter with a toaster on it. No, there's only a few angles where you can see it. It's fixable - just picking your shots."
Rhys and Russell 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.