The new parents took time out from changing nappies to meet the runners and organisers of the Ring O' Fire race, which takes place annually on the island.
The Duke and Duchess of Cambridge in Anglesey on Friday
The Duchess was described as looking 'absolutely gorgeous' by onlookers
She wore black skinny jeans, a sage jacket and platform heels and was described as looking "absolutely gorgeous" by locals attending the event.
It is expected to be one of William and Kate's final public engagements on Anglesey as the new father's time on the island comes to an end and the young family move to London.
William was acting as starter for the race, which has been described as an "ultra" marathon - a three-day, 135-mile foot race around the rugged coast of Anglesey.