Elizabeth Emanuel made her mark with Princess Diana’s wedding gown, but there was another version waiting in the wings…just in case

As Lady Diana Spencer climbed the steps of St. Paul’s Cathedral in London on July 29, 1981, to marry Prince Charles, her majestic wedding dress with its 25-foot train brought a royal fairy tale to life. But unbeknownst to the 20-year-old bride and the millions watching on television, the designers behind the now-iconic gown had crafted a second, mystery dress as a precautionary measure for any unforeseen circumstances.

“I was a bit neurotic, and I thought, ‘What happens if somebody breaks in and steals the dress or something spills or there’s a fire or it gets stolen?’ ” Elizabeth Emanuel, who famously created Princess Diana’s wedding gown with former husband David, tells PEOPLE exclusively in this week’s issue. “So I thought, ‘I’m gonna make a backup dress.’ “

Drawing inspiration from a pink gown that the Emanuels made for Diana to wear at a private ball a few days before her wedding, Elizabeth quietly got to work.

The spare dress differed greatly from the famous gown that Princess Diana wore on her big day, notably lacking a long train. The silk was white, “not the deep ivory that the royal wedding dress was made of” and the backup had “slim ones, more fitted to her arms” with frilly cuffs, Elizabeth says. Additionally, the intricate designs on the dress Diana wore were hand-embroidered by Elizabeth, whereas the fabric for the backup was ready-made.

Elizabeth Emanuel poses with her recreated spare wedding dress for Princess Diana in London on March 7, 2024.Lauren Fleishman; Hair & Makeup: Graziella Cawthorne Vella

The extra dress was never completed.

“I just thought, ‘If anything happens, we’ll finish it off and have it ready,’ ” says Elizabeth, adding that “it likely ended up on some sample rail. It probably got reused, torn up, thrown out, who knows?”

After searching through old sketches and thumbnail images from an old documentary, the 70-year-old London-based designer recreated the backup royal wedding dress for a unique purpose: to exhibit it at the virtual Princess Diana Museum.

“We never got to see that dress on Diana and thought it would be lovely to envision it,” says Renae Plant, the museum’s director and curator, who acquired it for an undisclosed sum. “You cannot put a price tag on history.”

Prince Charles and Princess Diana at their wedding on July 29, 1981.Shutterstock

As excitement — and intense pressure — mounted in the run-up to the royal wedding day in 1981, Diana found the studio to be an “oasis of peace,” Elizabeth says. “She would go upstairs and chat with all the seamstresses. She loved browsing through the rails because this was a new world for her.”

“I don’t think she’d been particularly into fashion before she met us,” she adds.

Elizabeth Emanuel’s scrapbook.Lauren Fleishman

Unlike the weddings of Prince William in 2011 and Prince Harry in 2018, where the designers for brides Kate Middleton (Sarah Burton for Alexander McQueen) and Meghan Markle (Clare Waight Keller for Givenchy) were unconfirmed until closer to the nuptials, the Emanuels’ involvement with Diana was widely known in advance.

“When Diana came in for a fitting, there would be hundreds of people outside waiting to spot her,” Elizabeth says. “We had to put shutters up on our windows, and we used to put bits of fabric, in different colors, in the bins just to throw the journalists off the scent. “

Reflecting on how she and David helped before the late Princess of Wales into her horse-drawn carriage on her royal wedding day, Elizabeth says, “We could hear the people outside cheering. Everybody was happy and smiling. It really was a fairy-tale wedding.”

Princess Diana and Prince Charles at their wedding on July 29, 1981.Terry Fincher/Princess Diana Archive/Getty