The Duke's eyes lit up when he saw the gift – a little onesie emblazoned with a picture of a helicopter and the words 'Daddy's little co-pilot'. William – an RAF Search and Rescue pilot stationed at RAF Valley, Anglesey – seemed delighted with the baby-themed present.
Samantha Hill, a 27-year-old new mum, from Sudbury, Suffolk, had made the cute babygrow. She had brought it along with her four-week-old daughter Beth, to meet the Prince and his wife the Duchess of Cambridge.
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."
William and Kate have made no secret of their desire to have a family. On the couple's trip to South East Asia in September, the Prince told schoolchildren he would like to have two children. The same month, Kate was said to be overjoyed to learn her favourite police bodyguard is expecting - and is reported to have told her: "You beat me to it."
Royal fans are hoping it's just a matter of time until a happy announcement is made by Clarence House – and William's delight over the onesie will only add to the anticipation.
Kate also got the chance to meet some cute babies during the couple's trip. The elegant brunette was captivated by little James William, who had been given his middle name in tribute to her husband.
The little boy's mum Tessa Davies, from Cambridge, described their meeting. "She said how cute he was. He was due on their first wedding anniversary," said the 35-year-old. "His name is James William - the William was named after Prince William. I told her that and she said that was wonderful."
She added: "I wrote to Prince William and Kate to congratulate them on their wedding anniversary and told them he was due on that date. I got a lovely letter back saying how pleased they were."
Sarah Wood, a student at St John's college, who was holding James, recounted: "She said 'hello cute little man'."
Kate was particularly taken with another baby – three-and-a-half- month-old Zachary Tiger Sargent. His mum Laura said: "She asked what his name was and how old he was and shook his hand. She seemed very interested in him."
Kate and William were in the historical university city from which they take their name, marking the first time the couple have travelled there together since they were decorated with titles after 2011's glorious royal wedding. Both were there to set up a shelter for Princess Diana's homeless charity, Centrepoint.
Swathed in a stylish beige coat by MaxMara, Kate looked elegant and seasonal as she and her husband arrived by train to carry out their series of engagements. Her newly-cut fringe offset the look perfectly, although she confessed to being "not sure" about her locks, which were whipped around by strong winds.