Child Bereavement UK is one of William’s key causes. Their center in Stratford, east London, which provides support for children and families facing grief, is marking its one-year anniversary.
William was just 15 when he lost his mother Princess Diana in 1997, and the charity’s founding patron, Julia Samuel, was a great friend of the princess. Her links with the family continue today, as she is also one of Prince George‘s godparents.
At one point during the visit, William comforted a little girl grieving for her father, telling her, “I lost my mummy when I was very young too.”
The prince asked 9-year-old Aoife, who lost her father to pancreatic cancer six years ago, “Do you know what happened to me? You know I lost my mummy when I was very young too. I was  and my brother was 12. So we lost our mummy when we were young as well. Do you speak about your daddy? It’s very important to talk about it, very, very important.”
Aoife said she told William that she had chosen reds, yellow, pinks and greens for a “memory jar” project at the center because her father liked bright colors and loved gardening.
“It was really nice that he talked to me,” she said. “It was like there are other people who know what it is like to lose someone.”
Aoife’s mother, Marie, told reporters, “I couldn’t believe it when he started to talk about his mother. It was very emotional and I was willing myself not to start to cry. I almost did.
“I am telling my children that if they take anything away from this day, it is what he said about how important it is to talk. Kids do not forget that. Sometimes it hurts but we can remember the happy things too. It is so important to talk.”
With their warmth and openness at visits like these, William and Kate “put people at their ease by being so warm and so open and cracking jokes,” Samuel tells PEOPLE. “You can see the terror in peoples’ eyes as they walk in, and you can see that fall away within a few minutes as people realize they are normal. That is always kind of touching to see
WATCH: Prince William and Princess Kate Support Grieving Families
“Also their depth of understanding of people. It is much more than a line, the surface of what a charity does — they really understand and care about the issues.”
She adds, “Bereavement — and particularly child death, which is so unbearable to think about — is something William is shining a light. He is helping us raise awareness in a way that no one else can do.
“That’s because people can see how authentic, and heartfelt, he is and he’s experienced it. People can pick up authenticity within seconds.”
William and Kate — who earlier on Wednesday bonded with mothers during a visit to highlight children’s mental health — joined a group of youngsters making the memory jars. The jars are filled with tightly packed layers of multi-colored salts, with each color representing a memory of their loved one.
Lorna Ireland, 36, and her son Shinobi Irons, 12, each filled their individual jars with bands of colored salt representing memories of the boy’s grandmother who died three years ago and godmother who died in 2015.
Ireland told reporters, “He told my son that when his mum died he was 15, at the time and he was very angry and found it very difficult to talk about it.
“So it was very important that Shinobi talked to somebody about how he was feeling even now years on.”
As well as providing vital support for children and families coping with loss, the charity also gives training for 8,000 professionals whose work brings them into contact with bereaved families.