updated 02/28/2012 AT 10:00 PM ET
•originally published 02/28/2012 AT 7:20 PM ET
The couple has welcomed a son in Santa Monica, a source confirms to PEOPLE. The new addition joins big sisters Seraphina, 3, and Violet, 6.
“It would be so weird to have a boy,” the actress told , but also said the experience would be “cool and different.”
In January, Garner and Affleck, both 39, were photographed walking arm-in-arm, with Garner sporting a sizable baby bump.
“He knows when to swoop in with the gesture. He’s sweet that way,” the actress says of her husband. “Honestly, I would do anything for that man, because I know it’s not taken for granted.”