Meryl Streep's oldest daughter, Mamie Gummer, has welcomed her first child, a baby boy, a rep confirms to PEOPLE

By Maria Pasquini
March 01, 2019 07:27 PM
Mamie Gummer and Meryl Streep
Brent N. Clarke/FilmMagic

Big congratulations are in order for Meryl Streep — and her daughter Mamie Gummer!

The 69-year-old actress has become a grandmother for the first time as Gummer, 35, and fiancé Mehar Sethi have welcomed a baby boy, PEOPLE confirms.

A rep for Gummer confirmed to USA Today in December that the actress — who shared the screen with her famous mother in the 2015 film Ricki and the Flash and 2007’s Evening — and Sethi, a 36-year-old producer, were expecting their first child together.

Streep and her husband Don Gummer have four children together: daughters Mamie, Louisa, 27, and Grace, 32, as well as son Henry Wolfe, 33.

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Mamie and Grace Gummer
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Meryl Streep
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Although Streep has already raised four kids, while filming her role in Mary Poppins Returns, the actress had a bit of a mishap while giving the child thespians an acting lesson on set.

“We were in the middle of my big musical number, and I was showing off,” Streep previously told PEOPLE. “I told them, ‘The first thing they teach you in drama school is how to fall down.’ “

“So I marched across the room and pretended to trip and fell down,” she continued.

Meryl Streep in Mary Poppins Returns
Jay Maidment/Getty

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Unfortunately, the three-time Oscar winner hit the ground a little too realistically.

“I did it so hard on both of my knees I practically broke them!” she said. “I thought, ‘Don’t be such a jerk, you’re not 11 years old anymore.’ “

US Weekly was the first to report the birth.