"Will you marry me, Katie?" the sign read.
Groom-to-be Peter Gallagher, 29, brought his girlfriend Katie Ellis, 28, to the aquarium Saturday afternoon for the prearranged event, the Boston Herald reported.
"I've been nervous for the past week. Very nervous," said Gallagher, who is a middle school teacher in Lakeville. "But I wouldn't have done this if I was afraid she'd say no."
Ellis, a fellow teacher, said yes.
"I'm really shocked. I don't have words," Ellis said a few minutes later. "I'm very happy."
"I knew it was coming but ... I thought it would be a month from now."
The couple have only been dating since December, but have known each other since they were teenagers, Gallagher said.
"It felt right," Gallagher said. "When it feels right, that's when you do it."
The aquarium isn't the only creative spot for proposals in Boston; last year, 62 men proposed to their girlfriends at Fenway Park front of Red Sox fans.
Swan Boats and Aerial Banner Co. are also popular outlets for those wanting to propose with style.
Celebrity Families of 2014 [PHOTOS]