The 36-year-old royal - who has Prince George, 5, Princess Charlotte, 3, and Prince Louis, nine months, with his wife Duchess Catherine - openly discussed the struggles of becoming a dad and the "fears" of having a newborn baby around.
During a visit to a Future Dads session, which helps to provide practical guidance and advice for fathers-to-be, he said: "The fear of having a newborn baby, that's very vulnerable and that's what you spend most of your time worrying about, thinking what do I do? And that's the thing isn't it?
"It's very daunting of how tiny they are when they first arrive. They are so fragile and everything's so tiny, their little fingers and toes, you do feel like if you move them around too much they're going to break almost but they don't!"
The Duke of Cambridge met with Rick Karadia-Hudson, who was attending the sessions ahead of the arrival of his first child in May, and Prince William drew on his own experience and quipped that it only got more hectic the older the child got.