Kate Winslet welcomed a son on Dec. 7 at a hospital in Sussex, County, U.K., People reports.
"Mother and baby are doing great," her rep told the magazine.
This is the actress' first child with husband Ned Rocknroll, whom she married last December. The couple announced that they were expecting in June.
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Winslet has a 13-year-old daughter, Mia, from her first marriage to director Jim Threapleton, and a 10-year-old son, Joe, with her second husband, Skyfall director Sam Mendes.
The Oscar winner, 38, will next be seen in the film Labor Day.