It's the fourth child in four years for the couple, who married in 2012.
"Our Baldwinitos are getting a new teammate this spring", Hilaria captioned a shot of herself, Alec, the family dog and the couple's children Leonardo "Leo" Ángel Charles, Rafael Thomas, and Carmen Gabriela.
Us Weekly spoke to the expectant mother after the gender reveal, and she admitted she was "in shock" when she discovered the baby was a boy. "I'm gonna make them a special cake to tell them if it's a boy or a girl..."
"I am the boss at home and everybody knows that".