Walsh, 34, gave birth Tuesday morning to an 8 lbs, 2 oz. baby boy. The couple have named him Kelsey Gabriel Elias Grammer, but will call him by his middle name.
"Our son will be called Gabriel as there is a tradition in our family of going by our middle names," Grammer, whose full name is Allen Kelsey Grammer, tells Entertainment Tonight. "We are blessed and excited to have this lovely young man join our family -- he is magnificent!"
Grammer, 59, and Walsh already have one child together, 2-year-old daughter Faith Evangeline Elisa. The couple married in 2011, and the actor has four other children from previous relationships. He is also grandfather to daughter Spencer's son Emmett Emmanuel.
Grammer will explore his family history on the new season of Who Do You Think You Are?.