After dating for more than a year, Scarlett Johansson is set to marry her boyfriend Ryan Reynolds, PEOPLE has learned exclusively.

"They're both thrilled," Johansson's rep Marcel Pariseau tells PEOPLE.

Reynolds, 31, currently filming the aptly named The Proposal in Boston with Sandra Bullock, recently popped the question to Johansson, 23. The couple have not set a wedding date.

The Nanny Diaries star is expected to show off her sparkler at Monday night's Metropolitan Museum Costume Institute Gala in New York. Sources say Johansson is eager to "show off her rock" with her Dolce & Gabbana gown.