Princess Diana’s Go-To Design House Says She ‘Used Her Dresses to Save Lives’

As Princess Diana’s life and work is commemorated by friends and associates alike 20 years after her death, another landmark is also being passed.

Diana’s favorite design house, Catherine Walker & Co,. is marking 40 years in business this month, and it’s fitting that the designer has the largest number of outfits chosen for inclusion in the special fashion exhibit at Diana’s former home Kensington Palace.

Catherine Walker, who died at 65 in 2010 after battling breast cancer, was with Diana from almost the beginning of the princess’s public life. She started designing her maternity wear when Diana was expecting Prince William and outfitted her with workwear suits and glamorous gowns for royal tours, right up to her death in 1997.

“Designing for the Princess . . . was about beauty and dreams,” she wrote in her autobiography in 1998. During the early days, Walker was surprised by two things: “The Princess’s ease and modesty, and the fact that despite the guidance she was given, nothing could really be enough for the awesome situation she was faced with.”

Eventually their working relationship had developed so intuitively that it “reach a point of shorthand,” she writes, and they were once given four days to come up with five new outfits when Diana “ran out of clothes” for the Australia tour of 1983.

Her last act was to provide a dress for Diana to be laid to rest in after receiving a call from Diana’s butler Paul Burrell with news of her tragic death. She created “the saddest and most difficult commission of my life.”

Today, the always impeccably discreet design house continues its links with royalty, dressing Princess Kate and some of the world’s most famous names, from Oscar winner Helen Mirren to actress Joely Richardson.

Said Cyrus, Walker’s widower and the head of design at Catherine Walker & Co., tells PEOPLE, “As with all our clients who are in the public eye and attend high profile events, we worked very closely with Diana to ensure what she was wore was appropriate and she — not the clothes — was the star.

“My wife and I spent a great deal of time researching what she wore for official visits abroad, even visiting countries in advance to make sure we had it right. We tried to ensure that our designs bridged her ambassadorial role for her own country and also paid respect to each destination.”

And they helped her make an impact, whether that was not wearing gloves so she could connect with people better or wearing warm colors on visits to hospitals. “She will always be remembered for her humanitarian work. In the end, she used her dresses to save lives,” Cyrus adds.

Among the showstoppers Catherine Walker created for Diana was the one she wore for a trip to Versailles in 1994. Eleri Lynn, curator of the Kensington Palace exhibit, tells PEOPLE, “The couturier Pierre Cardin was at the event and said ‘We are at Versailles, the home of the Sun King, and now we have the Sun Princess of Versailles.’ Diana was a very proud ambassador of British fashion.”

Cyrus explains, “In advance of the Princess’s visit we studied the interior of Versailles Palace, and we were struck by the way the light penetrated the building through the windows, each one set in relief with an ornate crenelated surround. We were therefore inspired to create a neckline that framed her face with gleaming bugle and round beads – allowing her to shine like the light from the palace windows.”

He adds, “The relationship between the House and Diana was positive and professional. We saw our job as giving her the tools of her trade. She was always very polite, very courteous and very appreciative. She was never late for an appointment and whenever she wore a dress that was admired, she’d thank us.”