On Wednesday, Kate, 32, was at Bletchley Park, the secret wartime spy base brought to life in the movie Enigma starring Kate Winslet. The base's historic huts where the code breakers worked have been renovated to look like they did 70 years ago.
And Kate looked the part. She dressed in a 1940s-style navy pencil skirt and cream outfit by Alexander McQueen and sapphire and diamond earrings that once belonged to her late mother-in-law, Princess Diana.
Kate's paternal grandmother, Valerie Glassborow, and her twin sister, Mary, worked in Hut 6 as duty officers in the "Cover Management Y" team that identified interception sites and signals that were suitable for monitoring. They would then pass the information on to code breakers.
The pair had come from administrative jobs at the Foreign Office.
When Kate met the twins' friend Lady Marion Body, 90, she wanted to find out all she could about the role Valerie – who later married Kate's grandfather Peter – played.
"When I was a young girl, I did ask Granny about it," she told Lady Body.
But like many of the era, she didn't pass along all their stories of wartime work.
"Valerie died a few years ago and it was only fairly recently that people felt able to talk about it," Lady Body tells PEOPLE. "She'd go and tell her father."
A key moment was when Lady Body told Kate of how they learned that the Japanese wanted to surrender. "We sat there in complete silence for about a minute before we were told to get on with our work. The duchess didn't know that story."
And she says of Kate, "She's lovely, she's absolutely wonderful."
Family ResemblanceLady Body also shared how Kate reminded her of the duchess's late grandmother. "There is a likeness, in her hair color. And possibly her eyes."
Explaining the work, she adds, "The radio stations called Y stations, we were listening and they used to send in, I think every 15 minutes, the call signs they were picking up and we had to check they were doing the right thing.
"The duchess's grandmother worked on the same desk as me. I had been at secretarial college with those two girls so I knew them very well ... They were fun, when you have such a boring job you had to get on well. We knew exactly what we were doing – it was part of the war effort."
Elsewhere in the center, Kate donned headphones and got some experience code-breaking and met veterans who were recalling the old days in the main building's library.
Chief executive of Bletchley Park, Iain Stranden, told PEOPLE: "Some jobs were glamorous and some were less glamorous. But everyone had an important part to play."
The work at Bletchley played a crucial role in bringing the war to an earlier end than would have otherwise been the case. Some historians believe that it shortened the war by two years.
"We are hugely privileged to have the duchess here," Stranden said. "With her family connections it makes it even more special."
Stranden explained that someone at the center discovered Miss Glassborow had worked there and, when they asked for a member of the royal family to launch the newly restored huts, they thought Kate would be the "perfect fit."
"As far as we know, the family knew of the connection but it wasn't in the public domain," he said. "Like most of the veterans here, the family have kept quiet about it."
"She was the right person to come and do it," Lady Body added of the Duchess's appearance. "The connection with her grandmother set the seal on it."