He and his wife, Penny Lancaster Stewart, welcomed their second son together, Aiden, on Wednesday. He weighed in at 7 lbs., 12 oz.
"Mother and baby are healthy and blissfully happy," a rep for the couple tells PEOPLE.
The new arrival also came just in time for Lancaster's birthday – she turns 40 in March.
Aiden is the eighth child for Stewart, 66, and the couple's second together – their elder son, Alastair Wallace, is 5.
"We were thrilled and delighted to be able to tell Alastair that he was going to be a big brother," the Stewarts said in August.