He recently returned to work in Anglesey as an RAF search-and-rescue pilot after his two-week paternity leave ran out. But, according to William, raising the new prince has been just as challenging a job.
“I thought search and rescue duties... were physically and mentally demanding but looking after a three-week-old baby is right up there,” he said at today's event.
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He also thanked the crowd for welcoming both himself and Kate, who made their "first home" on the island.
"I know that I speak for Catherine when I say I have never in my life known somewhere as beautiful and welcoming as Anglesey,” he said.
The prince's three-year tour of duty will come to an end next month, and royal officials will soon announce his future plans.
Meanwhile, the Duchess and newborn royal baby have been staying in Bucklebury at the home of Kate’s parents.
They haven’t been spotted since leaving Kensington Palace three weeks ago, but new royal baby photos are expected to be released soon.