Michelle Dockery, Downton Abbey Star, Flashes Sideboob at SAG Awards 2013

Actress Michelle Dockery attends the 19th Annual Screen Actors Guild Awards at The Shrine Auditorium on January 27, 2013 in Los Angeles, California.  Jason Kempin/Getty Images

What would the Dowager Countess have to say about this? Michelle Dockery was among the select stars of Downton Abbey on hand for the SAG Awards 2013 at the Shrine Auditorium in Los Angeles Sunday, Jan. 27 — where the BBC costume drama picked up the award for Best Ensemble, Drama.

But it was the 31-year-old British actress' chosen dress of the evening that really stole the show: a vintage Chado Ralph Rucci black satin gown with sheer panels that displayed a shocking amount of "side boob." (Dockery also sported a chic new bob hairdo, and accessorized the look with black satin Elba pumps by Rupert Sanderson.)

The star, who plays the more buttoned-up Lady Mary Crawley on the smash series, seemed unfazed by the exposure as she posed on the red carpet — causing major melee among enthralled photographers clamoring for Dockery to pose for more shots. At one point, Dockery giggled over the commotion and gave her publicist a knowing look.

After accepting the show's Best Ensemble SAG with costars Phyllis Logan (Mrs. Hughes), Dan Stevens (Sir Matthew Crawley, Mary's husband), Allen Leech (Tom Branson) and Sophie McShera (Daisy), Dockery told Us Weekly backstage that she's shocked American Downton fans for an entirely different sartorial reason.

"Once Laura Carmichael and I, who plays Edith Crawley, were out one evening in New York, and we ran into some fans," she explained. "The two of us were in jeans and leather jackets, and they could barely look at us both– because they were appalled that we were in modern clothes and not in fancy [period] dresses. It's just amazing, the response here. It's really wonderful."

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