Ben Affleck and Jennifer Garner
02/29/2012 AT 12:30 PM EST
, Seraphina Rose Elizabeth
and ... Samuel.
revealed the name of his and wife Jennifer Garner
's newest addition
– a son – Wednesday morning on his Facebook timeline
"We are happy to announce on February 27, Jennifer gave birth to a healthy baby boy, Samuel Garner Affleck," the actor, 39, writes.
The newborn, who arrived Monday, joins his elder sisters, ages 6 and 3 respectively.
"Our girls are working on names. At first they were definitely Disney. It was like, Donald Duck, Minnie Mouse Affleck,” the actress, 39, told Jay Leno recently
. "And then they've moved on. Then it was Peter Pan, Captain Hook, Smee."
The couple, married since June 2005
, announced the pregnancy