The making of Princess Diana's iconic wedding dress was a top-secret process, so it's no surprise that there was a codename involved.

In a bid to keep their secrecy and eliminate any chance of leaks, the wedding gown designers and their small, loyal staff would use the name when referring to their famous client or when she made phone calls, which was revealed in an upcoming documentary.

Diana went by Deborah Cornwall. Her surname was perhaps inspired by one of the royal titles she took upon her marriage to the future King Charles — the Duchess of Cornwall — although she was better known by her higher title of the Princess of Wales.

Ironically, her fake last name would become more closely associated with the future Queen Camilla, who had an affair with Charles during his marriage to Diana. Camilla opted to go by the Duchess of Cornwall title instead of the Princess of Wales title upon her 2005 wedding to Charles before becoming Queen in 2022.

The name is unveiled by one of the creators of Diana’s wedding dress, Elizabeth Emanuel, in a new documentary, Secrets of Diana’s Wedding Dress, which will air on 5 at 9 p.m. U.K. time on June 28.

"When we started to see Diana, we were just very aware of security, so we decided to call her Deborah. We called her Deborah Cornwall. Isn’t that strange?" Recalls Elizabeth, who was part of the design duo with then-husband David Emanuel.

It was all part of the elaborate plans that the couple put in place to keep news of the gown and their famous client a secret.

As they hoped to thwart the inquisitive — and sometimes intrusive — reporters who were trying to find out more about the dress, the couple employed two security guards, Bert and Jim, who took turns looking after the premises. They would also put different swatches of material in the garbage bins, hoping to foil any journalists who may have been tempted to sift through the trash. Staff were also offered cash by reporters to disclose information about the wedding gown.

Other precautionary measures included the preparation of a second wedding dress, just in case the first was revealed or something happened to it. PEOPLE revealed the story behind that dress in April 2024, when Elizabeth unveiled a completed version of it.

"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 told PEOPLE exclusively in April 2024. "So I thought, 'I'm gonna make a backup dress.' "

In the new documentary, Elizabeth remembers the day that Diana called the salon and ask if Elizabeth and David would do her “the honor” of making the dress — and the shriek of excitement that Elizabeth made when she was told (only having to make an excuse to the client she was serving at the time, telling a white lie about her brother expecting a baby).

As the design took shape, David recalls they couldn’t make an "understated dress. It had to be significant."

The seamstresses beavered away upstairs, and later, the mothers of both Elizabeth and her personal assistant Caroline Slocock were drafted in to help.

One day, Diana wanted to "acknowledge" the work being done. They would keep Diana from the workroom, but “one day, she had persuaded me to let her go upstairs. She was just curious and wanted to see everybody. They were almost crying,” when she did, Elizabeth says the documentary.

Elizabeth’s favorite picture of them creating the dress shows her peeking from beside the skirt as they make amendments.

“I can’t believe we managed to create the dress in that attic space,” she says in the documentary.

When the dress came together, they chose to add the longest train they could imagine, even calling up wedding venue St. Paul’s Cathedral to check to width and length of the aisle so they could be sure it would fit.

Elizabeth and David also speak about how in the weeks leading up to the wedding day, Diana lost weight — going down to a 23-inch waist — and, after altering the bodice more than once, they started it all again.

“It was an extraordinary dress at an extraordinary time in history,” David says in the documentary.

“It’s really dominated my life ever since,” Elizabeth, who has set up her own studio recently making outfits worn by singers Dua Lipa and Courtney Love, says.