Princes Diana's designer reveals archive of hidden gowns kept in boxes for decades: 'It’s very hard for me'

Though Diana never wore it in public, it was created from the same rare bolt of fabric as the black gown she famously wore on her first official engagement with Prince Charles in 1981 — a defining moment in her emergence as a style icon.

“I called it the Sister Dress because it came from the same bolt of fabric,” Emanuel said. “Diana tried it on. We were considering this, and others — some black with gold sequins — but we kept coming back to this one.”

Ultimately, Diana chose the more daring strapless version. “She’d been wearing these very romantic, pastel, frothy dresses,” Emanuel explained. “We thought this contrast would create a buzz, though we had no idea just how much. That black dress marked the transformation. She became a dazzling starlet in the making. From that moment on, she was a fashion icon.”

The Sister Dress remained unworn, stored away in darkness for decades. “I’m a hoarder,” Emanuel admitted. “It’s very hard for me to let anything go. But when I realised this was still around, I decided to keep it.”

The dress spent years boxed up at Hampton Court Palace, where Emanuel’s archive has been held. “It’s in amazing condition because it’s never seen sunlight,” she said. “It’s exactly the same fabric as the original, made by the same seamstress, Nina. All the workmanship is there. From a historical perspective, it’s really important.”

Alongside the Sister Dress, a collection of never-seen sketches and fabric swatches — some cut from the original royal wedding dress — will also go under the hammer at Julien’s Auctions in Beverly Hills on June 26.

Emanuel said she had long been reluctant to release them. “These dresses are memories,” she told the People's Chanel. “They’re part of my life. But I thought it would be nice to bring them out of the darkness — especially for people who loved Diana and everything she represented.”

Some sketches are accompanied by rare fragments of fabric. “That’s all I’ve got left of the Sister Dress material,” she said, pointing to a sliver attached to a new illustration.

“When it’s gone, it’s gone. But I wanted people to be able to see and feel it — to understand the craftsmanship, the history.”

The designer, who famously co-created Diana’s wedding dress with then-husband David Emanuel, also reflected on how the Princess’s style shaped a generation.

“She chose that wedding dress, and suddenly it became history,” she said. After asking Emanuel if Diana defined the style of the 1980s and early 1990s, she explained: "People copied her because she looked so good, and she had that rare charisma. You couldn’t define it, but you felt it the moment she walked into a room.”

Over the years, Emanuel designed dozens of outfits for Diana, including looks for her 1986 Gulf Tour, where modest dress codes inspired covered-up, high-neck styles.

“She inspired me so much,” Emanuel said. “I went over the top with the designs. She made me want to create more.”

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Though she’s created everything from ballet costumes to airline uniforms since then, it’s her work with Diana that remains most meaningful.

“How can you top that as a designer?” she said. “We were so lucky to be there at the beginning, when she was just forming her style. And then, in time, she found her confidence, and our job was done.”

Emanuel’s collection — a capsule of fashion, memory and royal history — will be auctioned by Julien’s Auctions in Beverly Hills on June 26.