The designer had to make an excuse to leave her client during a fitting so she could share the exciting news with her team

Princess Diana (left) and Elizabeth Emanuel (right) in June 1997. Photo: Tim Graham Photo Library via Getty

Princess Diana’s call to ask a big question to her wedding dress designer came at a slightly inconvenient time.

Elizabeth Emanuel, who with her ex-husband David designed the gown that Diana wore for her walk down the aisle in 1981 as she married the future King Charles, recalled the moment she realized her “life was going to change” at PEOPLE’s Styling Princess Diana panel at Fotografiska New York on May 21. Elizabeth was with a client for a fitting when the call came.

“The phone started to ring, and it rang and rang, and nobody was picking it up. I said, ‘I’m so sorry, I’m just going to have to take this call,’ ” the designer said. “And it was Diana. And she said, ‘It’s me,’ you know? ‘Would you do me the honor of making my wedding dress? You can’t tell anybody about this, there’s not going to be an announcement, so you’ve got to keep it very secret.’ “

She continued, “It was such a special moment because I thought, ‘My life was going to change, David’s life. It’s never going to be the same again.’ “

After hanging up, Elizabeth came up with an excuse for her client so she could tell her team the big news immediately: “My brother had a baby,” she fibbed.

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Elizabeth added during the panel that Princess Diana didn’t “have any idea” about what she wanted for her bridal gown. The designer explained she did “lots and lots of sketches” and also had Diana try on some ready-to-wear dresses, including one that became the template for the final product.

“A lot of it was trust, and she liked our style,” Elizabeth said.

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Princess Diana and Prince Charles at their wedding on July 29, 1981.Jayne Fincher/Princess Diana Archive/Hulton Royals Collection/Getty

Elizabeth plans to make a modern version of the late Princess of Wales’ iconic bridal gown.

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

The designer added of the “sequel” to the original gown, “It’s a really exciting thing because I often get asked, ‘Would you do the same dress again?’ Well, I wouldn’t change a thing on the dress in 1981, but if I was looking at it through my eyes now, there’s so many possibilities.”

Elizabeth Emanuel (left) and Princess Diana prepare for a royal tour on August 6, 1986.Tim Graham/Getty Images

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Unbeknownst to the 20-year-old bride and the millions watching on television in 1981, the Emanuels crafted a second wedding dress as a precautionary measure.

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

Diana’s spare outfit was never fully completed and “disappeared” in the years following the wedding after going unused.

After searching through old sketches and thumbnail images from an old documentary, Elizabeth recently recreated the backup royal wedding dress to exhibit at the virtual Princess Diana Museum.

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