Gotham City’s population is growing.
“She and Ben are very happy about this news,” a source tells PEOPLE of the Gotham costars. “Everyone is very excited.”
The former Homeland actress is already mom to 23-month-old Julius, her son with estranged husband, director/writer Austin Chick.
On Monday, PEOPLE confirmed the parents-to-be were dating after the two were spotted together at multiple events during Emmy Awards weekend, including the Fox party on Sunday, where they were seen holding hands.
This will be the first child for the former O.C. star, 37, while Baccarin, 36, and Chick welcomed their son in 2013 before he filed for divorce in July after three and a half years of marriage.
— Anya Leon with reporting by Blaine Zuckerman