Prince William tells Mary Berry he teaches his children about homelessness and other issues close to Diana's heart

The Duke and Duchess of Cambridge with Mary Berry Credit: BBC/Shine TV/Kensington Palace/PA

The Duke of Cambridge has said he tries to educate his children about issues that his late mother Diana, Princess of Wales, cared about.

Appearing as part of Mary Berry’s festive show, William said Prince George, six, Princess Charlotte, four, and Prince Louis, one, are already taking an interest in causes close to Diana's heart such as homelessness, revealing that on the school run, the elder two have asked of people living on the streets: ‘Why can’t they go home?’”

During a visit to The Passage, a homelessness charity based in London, which the duke supports as royal patron, William made cups of tea with the former Great British Bake Off judge.

William and Mary Berry at The Passage in London Credit: BBC/Shine TV/Kensington Palace/PA

William told her about visiting the project for the first time as a boy.

He said: “It was one of the first places I came to actually. I must have been between eight and 10, something like that. It had a profound impact on me.

“My mother knew what she was doing with it. She realised that it was very important when you grow up – especially in the life that we grew up – that you realise that life happens beyond palace walls, and that you see real people struggling with real issues.”

Mrs Berry replied: “Your mother chose the non-popular, the things we didn’t really talk about.

“I remember seeing her early on shaking hands with someone that had Aids, and it changed all our views.”

Kate decorates cakes with Mary Berry. Credit: BBC/Shine TV/Kensington Palace/PA

William said: “She liked to challenge the social norms about charities and about disadvantages and vulnerable people.”

Asked whether he educated his children about such issues, he said: “Absolutely, and on the school run – I know it sounds a little bit contrite – but on the school run already, bear in mind six and four, whenever we see someone who is sleeping rough on the street I talk about it and I point it out and I explain.

“And they are all very interested. They are like: ‘Why can’t they go home?’”

A Berry Royal Christmas also sees TV star Berry show Kate how to decorate cakes and mix a non-alcoholic cranberry juice cocktail.

Kate served the drink at The Brink, a dry bar set up by the charity Action on Addiction in Liverpool, of which she is patron.

William, Kate and Mary Berry with Bake Off winner Nadiya Hussain Credit: BBC/Shine TV/Kensington Palace/PA

“It reminded me of my university days when I did a bit of waitressing,” she said.

Asked by Berry whether she was any good, the duchess replied: “No – I was terrible.”

Berry and the duke know each other through their support of Child Bereavement UK, and the show came about as the celebrity cook wanted to learn more about the duke and duchess’s charities, particularly Kate’s work supporting the early years development of children.

In the hour-long programme, she prepares some of her favourite Christmas recipes to inspire the television audience, and at the end of the show is joined by special guests, including Nadiya Hussain, as she makes festive food for charity workers.

A Berry Royal Christmas airs on December 16 at 8.30pm on BBC One.