One of Prince Louis' earliest words was "Mary" after he recognised TV chef Mary Berry on a cookbook, the Duchess of Cambridge has said.
Catherine told the story to the former Bake Off presenter in a BBC Christmas special, which airs on Monday evening.
She said 19-month-old Prince Louis, was "fascinated by faces" and would say "that's Mary Berry" when he saw her on cookbooks in the family's kitchen.
Berry helped Prince William and Catherine prepare for a charity event.
"One of Louis' first words was Mary, because right at his height are all my cooking books in the kitchen bookshelf," Catherine tells the cook on A Berry Royal Christmas.
"And children are really fascinated by faces, and your faces are all over your cooking books and he would say 'That's Mary Berry'... so he would definitely recognise you if he saw you today."
The duchess also shared snippets of family life, including how the family uses Berry's recipes when making pizza, which the children "loved".
Asked by Berry if she cooked with the children, she replied: "Yes, I really enjoy it. Again, for them to be creative, for them to try and be as independent as possible with it."
Prince William was also interviewed by Berry on the programme and spoke about how his relationship with his mother, the late Princess Diana, had influenced his style of parenting.
Speaking at homelessness charity The Passage, in London, Prince William said the centre was one of the first places to which he made an official visit and it had had a "profound impact" on him.
"My mother knew what she was doing with it," he said.
"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."
He added that his mother "liked to challenge the social norms about charities and about disadvantages and vulnerable people".
Asked whether he speaks to his children about such issues, he told how Prince George, six, and Charlotte, four, would quiz him about the world on the way to school in south-west London.
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 (George and Charlotte's age), whenever we see someone who is sleeping rough on the street I talk about it and I point it out and I explain."
During the programme, Berry helps the Duke and Duchess of Cambridge prepare food for a royal event held to thank all those working and volunteering over the festive period.
In one scene, Kate serves non-alcoholic cocktails to people at a dry bar in Liverpool which has been set up by the charity Action on Addiction.
"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."
The programme, which culminates in a Christmas party hosted by the royal couple, also features some of Berry's favourite Christmas recipes.
There is also a special guest appearance from Nadiya Hussain, who won Bake Off in 2015 when Berry was a judge on the show, which is now broadcast on Channel 4.
Berry described the charity work carried out by the Duke and Duchess of Cambridge as "remarkable".
"They don't just arrive and shake a few hands make a few smiles and a speech, they want to get involved, and they want to see what they can do," she said.
"And it isn't just one visit, they come back again and ask for the results and they remember who they spoke to last time. I think that's remarkable."
A Berry Royal Christmas airs on Monday 16 December at 20:30 GMT on BBC One