The new father had his first day out since the Duchess of Cambridge gave birth, to play at a polo match with his brother, Prince Harry.
Prince William, 31, scored a winning goal for his team, but said his mind was not entirely on the match.
"I was in baby mode out there, thinking about nappies, I wasn't really in the zone," he was quoted by The Telegraph as saying.
The prince said it was "good to get out of the house" for an afternoon.
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He and his wife are understood to be staying with her parents in Bucklebury, Berkshire.
"I've got to make sure I'm not too late back," William was quoted by the daily as saying.
And asked about son George, who was born on July 22, he said: "He likes to move around a lot, he wriggles a lot, he keeps us on our toes."
Kate attended last year's match, along with the couple's puppy Lupo, to support William and Harry, but there was no sign of her yesterday.
On Friday Kensington Palace announced that the birth of the third-in-line to the throne had been formally registered after a registrar from Westminster City Council visited the palace.
William, signed the birth register entry for his son, listing his and wife Kate's jobs as prince and princess of the United Kingdom.
His next official public engagement will be to visit the Anglesey Show later this month.
An announcement on his future plans is expected within the next fee months.