The future King was visiting the National Football Museum in Manchester with his wife Kate when he opened up about their 17-month-old daughter and their three-year-old son Prince George.
"Charlotte is the one who shows more aptitude [for soccer]," William said, chatting to the England women's team captain, Steph Houghton, and her teammate Jill Scott. "George is sort of getting into it slowly, but Charlotte is showing more aptitude."
"They're great," he added.
William and Kate, both 34, were given a tour of the museum and shown some of the most special displays – including the 1966 World Cup football and the beloved trophy.
The Prince looked genuinely awestruck, and slightly nervous, as he was given a pair of gloves and asked to hold the orange leather ball. William declined holding the trophy, saying he didn't want to "jinx it".
The royals were introduced to one of the team members who kicked it, Roger Hunt, 78, who came to the engagement with his medal. The retired sports star asked William if he still played soccer.
"I play a little bit," said William, who is an Aston Villa fan. "At school and university mostly. Rugby I've stopped, too many injuries. I do a bit of swimming as well."
"We do quite a bit of running around after our kiddies," Kate added.
Dr Kevin Moore, director of the National Museum of Football, who showed them around, said afterwards: "The Duke chatted very knowledgeably as you would expect about football, but the Duchess did as well. She was very interested and knowledgeable about aspects of the game. She's also fully aware of her husband's great pride and support for Aston Villa."
William and Kate spent the day in Manchester carrying out four engagements in total. After their museum visit they took part in a wreath-laying ceremony to honour Manchester's six Victoria Cross recipients as part of the First World War Centenary campaign.
The royals then stopped by The National Graphene Institute at The University of Manchester where they helped seal a time capsule, followed by a visit to Francis House, a hospice that cares for children and young adults which was first opened in 1991 by William's late mother Diana.