The tot, whose name and other details have not been revealed, was born Saturday at Cedars-Sinai Medical Center in Los Angeles, according to E! News. He's little brother to 5-year-old Nahla, Berry's daughter with model Gabriel Aubry.
"Nahla visited her baby brother earlier today," a source told People on Saturday.
"This has been the biggest surprise of my life, to tell you the truth," the 47-year-old "X-Men" star told CNN in April, shortly after her pregnancy went public. "I thought I was kind of past the point where this could be a reality for me. So it's been a big surprise and the most wonderful."
Martinez and Berry, who met while working on the film "Dark Tide," got married in France in July.