03/26/2007 AT 08:00 AM EDT
When Grey's Anatomy
hunk Jeffrey Dean Morgan hooked up with his Weeds
costar Mary-Louise Parker, he also got a new man in his life: Parker's young son, William.
"We get along like peas in a pod," Morgan, 40, told PEOPLE about the 3-year-old when he and Parker, 43, attended Thursday's Broadway opening of the new musical Curtains
. (William's father is Parker's ex, Billy Crudup.)
Asked how William was doing, Parker replied, "Fantastic." But on the subject of how well her two guys get along, Parker – who earlier this month told PEOPLE
that her relationship with Morgan is "going great" – demurred to her date. "You'll have to ask him for yourself," she said.
"He's wonderful," replied Morgan. "He's great. We spend a lot of time reading, actually. And I just got back from the park [with him] before we came here."
Being around a child, Morgan admits, "It's a whole new world, a different world, but it's fantastic. It's great!"