The royal reportedly couldn't find an answer about the 92-year-old Queen's eating habits.
'You know, that’s such a good question. I don’t know,' Kate responded.
'I don’t know. Maybe next time I see her, shall I ask?'
The Duchess also revealed her children Prince George, aged five, and Princess Charlotte, 3, would be 'jealous' if they knew their mum was making pizza while they were at school.
'George and Charlotte would love to be learning outside the classroom,' she said of her two eldest children. 'It's still fun inside, but it's much better outside.'
When she was asked what Prince George was learning about in school, Kate told the children: 'He's learning about space.'