Kate attended the Ring O' Fire Anglesey Coastal Ultra Marathon with Prince William near their Anglesey home.
The Duchess was expected to make her first public appearance next month at a charity event for Tusk Trust, of which William is patron, but decided this morning that she would attend today.
The new mum met volunteers, runners and their families at the event that circumnavigates the island which the couple have called home for several years. She chose Paige jeans and a Zara top - which she also wore during her pregnancy - for the occasion.
They will soon leave Wales to take up permanent residence at the newly refurbished Kensington Palace.
Prince George was tucked up at home, and it is not clear who was on babysitting duty. Our money is on Carole, who has been a regular guest at the couple's Welsh home in recent weeks.