Sean Penn and Charlize Theron attend the "Charles James: Beyond Fashion" Costume Institute Gala at the Metropolitan Museum of Art on May 5, 2014 in New York City. (Photo by Kevin Mazur/WireImage) Credit: Kevin Mazur/WireImage

Sophisticated and sweet! Charlize Theron and Sean Penn looked effortlessly glamorous as they walked the red carpet together at the Metropolitan Museum of Art's Costume Institute Gala in New York City on May 5.

Theron, 38, beamed in a strapless Dior Haute Couture white crepe gown with navy and black satin incrustations. The actress paired the dress with a Dior black wool jacket and Dior clutch.

Prior to hitting the carpet, the blond shared her ensemble on her Instagram account, asking fans their opinion with the caption: "What do you think? #metgala #dior."

Penn, 53, opted for a traditional tux and white shirt. The Milk actor stayed close to his lady love, holding her hand as they made their way into the ball, which this year is celebrating the opening of the Charles James: Beyond Fashion exhibition. PHOTOS: See the best dressed stars at the Met Gala through the years

The Monster actress and Penn were first spotted out together in early January when they vacationed in Hawaii. Since then, the Oscar winners have attended several events together and been caught packing on the PDA.

According to a Jan. 18 blog post by Piers Morgan, Penn's described Theron as "a keeper."