Congratulations are in order — Mamie Gummer is a mom [1]! The 35-year-old actress gave birth to her first child, a baby boy, her rep confirmed to Us Weekly on Thursday. Mamie — who is Meryl Streep's eldest daughter [2] with husband Don Gummer — is engaged to screenwriter Mehar Sethi and their baby news [3] was first revealed this past December. Meryl shares four children with Don — daughters Louisa, Grace, and Mamie and son Henry — and this is the couple's first grandchild.

Mamie and Mehar got engaged this past August following her 2013 split from ex-husband Benjamin Walker. Mamie currently stars as Lucy Purcell in the HBO hit series, True Detective.