Mamie Gummer and Ben Walker
10/20/2009 at 08:00 AM EDT
Get ready for an acting dynasty: Actress Mamie Gummer, Meryl Streep's daughter, is engaged to stage actor Ben Walker, she told PEOPLE at the annual Whitney Gala Monday night, sponsored by Versace.
And he did on the old-fashioned way – on one knee.
"Yeah, he sure did," Gummer, 25, said, adding that her family is ecstatic. her dad is sculptor Don Gummer. "They're all very happy … we're very, very smiley."
Walker, 27, who proposed on Sunday, admitted he was scared, but Gummer said the proposal "was great."
Wearing a modest engagement ring with an old-fashioned setting that was slightly oversized, Gummer (who's gone by the nickname Mamie instead of her given name of Mary Willa since she was a baby) said where her fiancé got it from before popping the question is a secret he won't even share with her.
"He had it made somewhere," she said. "He won't tell me where, so I doubt he will tell you."
The two met while performing in Dangerous Liaisons on Broadway in April 2008,and began dating a year and a half ago. "He was the Keanu to my Uma," she said. "We were kind of pals first. It was a drawn-out thing."
So why did she fall for the towering hunk? "We'll, look how tall he is," she said. "He's very nice. He puts up with me. And he's very patient."
And he's good a relieving her stress, she added. "He's really good at rubbing my jaw," she said. "I carry a lot of tension in my jaw."