"One of Louis' first words was 'Mary' because right at his height are all my cooking books in the kitchen bookshelf," the mother-of-three tells Berry during a sneak preview of the upcoming programme.
She added, "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."
In the hour-long special, the Duke and Duchess of Cambridge join Berry in preparing festive food to thank those working and volunteering over the Christmas period.
To mark the show's upcoming launch, Kensington Palace shared a clip from the show via Instagram which shows Prince William at Passage Charity with the British baker - an organisation which he first visited back in 1993 alongside Prince Harry and Princess Diana.
Since opening in 1980, the charity has helped over 130,000 people through its resource centre and homelessness prevention initiative.
During the clip, the Duke of Cambridge opens up about the ways in which he is teaching Prince George and Princess Charlotte about homelessness.
"On the school run, it sounds a little bit contrite, but on the school run already - bear in mind they're six and four - whenever we see anyone sleeping rough on the streets, I talk about it and I point it out and I explain why and they're all very interested," he revealed.
A Berry Royal Christmas airs on Monday at 8.10pm on BBC One in the UK.
