Introducing Grandma Meryl.
The family’s new addition is the first grandchild for Streep, 69, and her husband Don Gummer.
News of 35-year-old Mamie’s pregnancy was confirmed in December. The “True Detective” star has been engaged to Sethi Mehar since August.
Mamie and Streep starred alongside each other in mother-daughter flick “Rickie and The Flash,” in 2015.
The “Mama Mia!” actress and Don share three other children; Henry Wolfe Gummer, 39; Grace Gummer, 32, and Louisa Gummer, 27.
A rep for Gummer didn’t immediately respond to our request for comment.