New mum Samantha Hill gave the Duke a handmade babygrow as he chatted with his admiring public during a walkabout - which immediately sparked rumours that the Duchess of Cambridge might be keeping mum about a certain something.
The Duke took the babygrow and thanked Samantha, saying: "I'll keep that!"
William made the comments as he and wife Kate visited Cambridge - their first visit to the city that bears their name.
Samantha, 27, from Sudbury, Suffolk, was with her four-week old daughter Beth, when she handed William the babygrow bearing the slogan: "Daddy's Little Co-Pilot."
She said: "I made it for when his little one comes along, he's a helicopter pilot so his baby will think his daddy is cool.
"When I gave it to him he said 'I'll keep that' and handed it to his aide."
They met several babies and young children during their day out today as they visited Cambridge's Guildhall, the city's world-renowned university, a homeless shelter, school and nearby Peterborough City Hospital.
And, on her way from the Guildhall to the university, Kate tickled one baby's foot as she spoke to mother Tessa Davies, 35.
Tessa, who had given her seven-month-old son James the middle name William in honour of the Duke, said: "She said how cute he was. He was due on their first wedding anniversary.
"His name is James William - the William was named after Prince William. I told her that and she said that was wonderful."
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