Speaking at the opening of the new Magic Garden play area at Hampton Court Palace, Kate told some of the gathered children that the pair have a royal hamster named Marvin, and it's a particular favourite with Princess Charlotte.
'She said she has a hamster and Charlotte really likes it because the whiskers always tickle her face,' nine-year-old Darcy recalled.
The Cambridges already have a dog, a spaniel named Lupo, who was a gift from Kate's brother James following her marriage to William in 2011, but it appears that the hamster may be a newer addition to the family.
The conversation seemed to make Kate nostalgic for her own childhood pets, as she also revealed that she'd had guinea pigs as a child - a pair named Salt and Pepper.
During her visit, Kate was keen to explore the park, adding that George would 'love' the space, but would probably be 'a bit scared' of the 25ft plastic dragon that was built as part of the new design.
The chairman of Historic Royal Palaces, Rupert Gavin, said that she was 'bowled over' by the gardens. 'She could immediately see just how wonderful it was and has said she really is looking forward to bringing her own children.'
The visit was part of a busy day of engagements for Kate - that afternoon, she attended an event as a Patron of the Anna Freud Centre, a charity that she supports as part of her her keen interest in children's mental health issues.
Peter Fonagy, Chief Executive of the Anna Freud Centre, said: 'I am honoured that the Duchess of Cambridge has chosen to become a patron of the Anna Freud Centre. I'm particularly proud because I have come to recognise just how knowledgeable she is in relation to what is a complex and difficult issue that so few people genuinely understand.'
Later that evening, Kate changed into her third outfit of the day to view photographs from her recent British Vogue photoshoot at the National Portrait Gallery.
The 34-year-old chose an elegant pink Alexander McQueen dress for the occasion, which was the first time she had seen the portraits of herself displayed.
Commenting on the picture of herself leaning over a fence, Kate told photographer Josh Olins: 'It was such a lovely moment, a beautiful end to the day. It didn't seem like January.'