Published Tuesday, 21 August 2012
The Downton Abbey star's wife Susie showed off her pregnancy bump on the red carpet of London's Olivier Awards in April, and Stevens has now revealed they recently became parents again.
He tells the Daily Telegraph: "Baby two has now arrived - it's a boy - and we are of course delighted. If you had done the maths it would be very odd if the birth hadn't happened by now."
The couple is already parents to daughter Willow, two, and the family is now heading to New York where Stevens will make his Broadway debut in The Heiress.
He adds: "We're going over to New York as a family so we'll all stay in an apartment somewhere, but I don't know where yet.
"We go there in a few weeks, to start rehearsals - it is all very exciting. We start previews in the beginning of October and then open in November."