Kate, looking striking in a £762 red woollen blazer by Lorenzo Serafini and skinny black jeans, joined the 36-year-old father-of-three, who looked delighted to be touring the helicopter base - even if the weather didn't quite play ball.
Yesterday, the Duke and Duchess of Cambridge told the world they were thrilled with the new arrival in the royal family, with William cheekily joking that he was looking forward to welcoming his brother to the 'sleep deprivation club'.
The royal, who worked for three years at RAF Valley on Anglesey from 2010 to 2013, made the trip north - on a soggy day - to re-acquaint himself with the invaluable work being done by the search and rescue helicopter team and Wales Air Ambulance in the region.
The unit William worked on has now moved from the island to the new base, Caernarfon, on the mainland and is run by Bristow Helicopters, which took over the contract from the military, but still has some of the same crew from William's time as a helicopter pilot.
William told his old crew that he does miss his old job, which involved flying rescue missions in all kinds of weather and terrain.
Coastguard helicopter winchman Paul Jones and his wife Gemma, were with their son's, Finlay, 12, and Alex, aged nine, who were much younger the last time Kate and William saw them.
Mr Jones said: 'It's lovely to see him, we worked very closely for three years and then he moved away. It was like he's never been away.'