“I call it the dress that never was,” designer Elizabeth Emanuel, who recently recreated the spare gown, tells PEOPLE

Princess Diana had no idea that the design team behind her royal wedding gown secretly created a second look for the wedding of the century.

The late Princess of Wales instantly made fashion history when she climbed the steps of St. Paul’s Cathedral in London to marry Prince Charles on July 29, 1981, her majestic wedding dress with a 25-foot train. But unbeknownst to the royal bride and the millions watching the fairy tale unfold on television, Elizabeth and David Emanuel crafted a backup bridal gown for any unforeseen circumstances.

“Neither of us wanted to worry her. It was a complete secret,” Elizabeth tells PEOPLE exclusively in this week’s issue.

The 70-year-old designer, who is based in London and continues to create couture, says she made the spare dress out of an abundance of caution before the big day.

“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 says. “So I thought, ‘I’m gonna make a backup dress.’ “

Elizabeth Emanuel with a recreation of the spare wedding dress in 2024; Princess Diana on her wedding day in July 1981.Lauren Fleishman; PA Images/Getty Images
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The spare gown greatly differed from Diana’s iconic bridal gown, notably lacking the long train. “It’s what made the dress so spectacular — it’s larger than life,” Elizabeth says of the fashion statement.

The second dress’ silk was also white, “not the deep ivory that the royal wedding dress was made of” and featured “slim” sleeves “more fitted to her arms” with frilly cuffs, in a tweak from the puff sleeves on Princess Diana’s gown. Elizabeth further hand-embroidered the designs on the dress Diana wore, while the fabric for the backup was ready-made.

The design itself was inspired by a pink gown that the Emanuels created for the bride to wear at a private ball a few days before her wedding, though the spare was never finished.

“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?”

“I call it the dress that never was,” she says.

Elizabeth Emanuel’s recreated version of Princess Diana’s backup wedding dress.Lauren Fleishman
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After scouring old sketches and thumbnails from an old documentary, the designer reproduced the backup bridal gown she made with her former husband for a unique purpose: presentation 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 the museum’s director and curator Renae Plant, who acquired the recreated piece for an undisclosed sum. “You cannot put a price tag on history.”

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

Over 40 years ago, Elizabeth says that the future Princess Diana found the studio to be an “oasis of peace” amid the excitement and mounting pressure leading up to her royal wedding day.

“She would go upstairs and chat with all the seamstresses. She loved browsing through the rails because this was a new world for her,” she says.

As the reimagined backup is readied for shipment to California, Elizabeth reflects on the royal wedding day moment she and David helped Diana before she moved into her awaiting carriage.

“We could hear the people outside cheering. Everybody was happy and smiling,” she says. “It really was a fairy-tale wedding. “

Princess Diana and Prince Charles on their wedding day in July 1981.Terry Fincher/Princess Diana Archive/Getty

Next on Elizabeth’s list is creating a modern reinterpretation of Princess Diana’s original wedding dress, which was most recently displayed at Kensington Palace in 2022, on loan from her sons Prince William and Prince Harry.

“I’m going to try and capture the spirit of the original — but through my eyes now,” Elizabeth tells PEOPLE. “I want to preserve all the sparkles and pearls but with a completely different vision.”