The 31-year-old played in the Audi Polo Challenge at Coworth Park, Ascot, Berkshire, with his brother, Prince Harry, and scored the winning goal for his team, but said he wasn't focused on the game.
"I was in baby mode out there, thinking about nappies, I wasn't really in the zone," he revealed to the press, but added it was "good to get out of the house" for an afternoon.
William was presented with a mini polo mallet for his son after the match and jokingly asked if the gift was diapers, because, "I've got to pick some up on my way home."
Speaking to guests after the match, William admitted, "I've got to make sure I'm not too late back," and when asked about his son, who was born on July 22, he confided, "He likes to move around a lot, he wriggles a lot, he keeps us on our toes."
Reporting by SIMON PERRY
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