Prince George, Princess Charlotte and Prince Louis, had a close bond with their great-grandmother, and Kate has previously spoken about Her Majesty's sweet tradition for her great-grandchildren whenever they went up to visit.
In her first solo TV interview for the 2016 ITV documentary, Our Queen at 90, Kate revealed the monarch's love for her family.
WATCH: Kate Middleton reveals how Prince Louis reacted to the Queen's death
Speaking about her daughter Charlotte's birth, the Duchess said: "The Queen was really thrilled that it was a little girl and I think as soon as we came back here to Kensington, she was one of our first visitors here. I think she's very fond of Charlotte. She's always watching what she's up to."
She added: "George is only two and a half and he calls her 'Gan-Gan'. She always leaves a little gift or something in their room when we go and stay, and that just shows her love for her family."
The Cambridges would visit the Queen at her Scottish estate during the summer and spend Christmas with the monarch at Sandringham, staying at their nearby country home, Anmer Hall.
The Queen had a close bond with her great grand-children
The monarch's great-grandchildren will no doubt miss her, although during a walkabout in Sandringham, Kate confessed that she believed only George fully understood what had happened.
And during a walkabout in Windsor, she revealed Prince Louis' sweet words after she broke the news of the Queen's death to him.
Speaking to a well-wisher, she said: "My little Louis is just so sweet. He said, 'Mummy don't worry, because she is now with great grandpa.'"
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