WHEN “The Twilight Saga: Breaking Dawn — Part 1” opens on Friday, fans won’t be at all surprised to see Edward utter, “I do.” They already know the plotlines of the books better than their own ancestries. But there is one mystery — the design of Bella’s wedding dress — that has “Twihards” all astir and the studio behind the film, Summit Entertainment, as tightlipped as a sorority pledge.

The studio is betting that, as with other wedding gowns that have made it to the big screen, thousands of fans will want a copy of the dress for their own big day. To that end, Summit has taken the unusual step of licensing the design to a mass-market bridal retailer.

To whet appetites, the studio has been ever so slowly reeling out snippets of the dress. Back in mid-June, it placed a crumb of information on Twitter that Carolina Herrera had designed the gown, a piece if news that quickly made its way to wedding and fashion blogs.

Summit also released a still of the actress Kristen Stewart as Bella Swan on her big day. The close-up photo showed about a square inch of her wedding veil — alas, not even enough material to determine if it was lace or tulle.

You’d think it was another royal wedding.

Since the still’s release, even Mrs. Herrera, brought on by the “Twilight” author, Stephenie Meyer, hasn’t revealed so much as a silhouette or a neckline. Mrs. Meyer’s 2008 book, “Breaking Dawn (The Twilight Saga, Book 4),” offers only quick glimpses of the dress, like “a long line of pearl buttons” up the back.

“I wanted the dress to have a period feel without being actually vintage,” Mrs. Meyer, who collaborated with Ms. Herrera, said in an e-mail.

Mrs. Herrera, whose gowns typically begin at $4,000, was equally cryptic in an e-mail: “Of course, I was inspired by Stephenie’s description of the gown in the book,” she wrote. “I also took into consideration the personality and the style of the bride.”

After being sent repeated e-mails asking for an image of the dress, Eric Kops, Summit’s senior vice president for publicity, responded: “We are saving the reveal of the dress as a surprise for the fans when they see the film. Therefore, we aren’t planning to release any images showing the dress until after the film in theatres.”

Beginning Nov. 21, just three days after the movie opens, wanna-be Bellas can get authorized copies of the gown for $799 in 400 bridal shops, including 67 Alfred Angelo stores.

Denise Wash, the vice president for marketing at Alfred Angelo, said that the company’s version will be “more forgiving” in its cut to flatter brides of all sizes, up to 30. In an interview with Cineplex.com this past July, Ms. Stewart commented: “The dress was tight. It was so tight.” The designers of the copy also substituted Italian lace used in Mrs. Herrera’s gown with a less lavish grade.

Mrs. Wash said that the gown “had a secret code” throughout its development. The company manufactured the design at its own factory in China. “It was like working for the C.I.A.,” she said.

Alfred Angelo has a history with Hollywood. In 1950, the company sold a copy of the “Father of the Bride” wedding dress worn by Elizabeth Taylor in the film.  The advertisement for the gown announced, “For Your Starring Moment.”

That symbiotic relationship between the film and fashion industries certainly predates Miss Taylor’s cinematic turn in tulle. Nearly two decades earlier, the elaborate bias-cut sheath worn by Claudette Colbert in the 1934 romp “It Happened One Night” made brides-to-be blush with envy.

“Within six months of the movie being released, there were, in stores across the United States, copies of that wedding gown with hang tags saying, ‘As worn by Claudette Colbert,’ ” said Sandy Schreier, the author of “Hollywood Gets Married.” “The studios had deals going with the manufacturers on the East Coast.”

Summit is no slouch when it comes to licensing this supernatural love triangle. Among dozens of other franchise-related products, the studio recently merchandised the coifs of “Twilight” with a line of hair tools like the Bella curling iron, which at $24.99 could be the perfect shower gift for any prospective bride holding her breath until the movie opens.