Congratulations to Meryl Streep on her new role: grandmother. The Oscar-winning actress became a grandma this week for the first time after her eldest daughter, 35-year-old True Detective star Mamie Gummer, gave birth to a boy, US Weekly reports. The boy, whose name has not been disclosed, is Gummer's first child with fiance Mehar Sethi, 36. Gummer was previously married to actor Benjamin Walker, but they broke up in 2013 after two years of marriage, E! Online reports. Streep, 69, has two other daughters, Grace, 32, and Louisa, 27, as well as 37-year-old son Henry. (More Meryl Streep stories.)