People magazine reported Tuesday that Journey River Green was born on Aug. 4.
Fox and Green are also the parents of Noah Shannon, 3 and Bodhi Ransom, 2. Green has a 14-year-old son named Kassius from a previous relationship.
E! News, which also announced the birth of the newest addition to the family, said Fox surprised fans at 2016 Cinema Con in the spring when she showed off a baby bump months after filing for divorce from Green, her spouse of five years.
The formerly estranged couple have reportedly since called off their divorce plans.