Credit: Michael Rozman/Warner Bros.

To honor his son Walker's first birthday, Private Practice star Taye Diggs got a new tattoo.

He shows off the ink — WALK, it reads on his forearm — on The Ellen DeGeneres Show Thursday (check your local listings).

"He's great," the star, 39, gushes.

He says he and his wife of seven years, actress Idina Menzel, often rap to their baby when they're changing him.

"He gets a kick out of that unless Idina and I are so self-involved that we get caught up in who's got the harmony and who's coming in late," he says. "He's like, 'I'm covered in feces! Can you just change me?'"