A source told Life & Style magazine: "She's glowing -- and so happy. They wanted to add another child to their family, and now they've got that! They're in a real good place."
A spokesperson for the couple confirmed they are expecting another baby, but did not say when the new arrival is due.
‘Grey’s Anatomy’ star Eric – who married Rebecca in 2004 – recently admitted he finds his wife even more attractive since she gave birth to Billie.
He said: "I don't know if there's any change more significant that a human being can make than that of a woman becoming a mother. There's no change more dramatic.
"You know, I'm a hundred times more attracted to her now and I love her exponentially more than I did before. It's just great to see her be a mother."
Eric also spoke of how much he enjoys taking his daughter to the park and seeing how much she enjoys the experience.
He said: "I like watching her laugh. Seeing this kid laugh when you put her on the swing, or slide down the slide with her, it's just. She owns me."