The Duchess of Cambridge will join Prince William when he starts the Anglesey ultra marathon today.
But the royal couple will appear without Prince George.
The Duke of Cambridge will start the Ring O'Fire Anglesey Coastal Ultra Marathon on Anglesey later. The Ultra Marathon is an annual 135 mile coastal marathon circumnavigating the Isle of Anglesey. The foot race is staged over three days and follows the Anglesey Coastal Path around the island.
Prince William will meet a number of runners and their families and a selection of volunteers involved in the administration of the race before officially starting the Ultra Marathon.
The 135 mile distance and 13,695 feet of vertical ascent makes the Ring O' Fire one of the most extreme ultra marathons in the United Kingdom.
Prince William is to leave his home and his job as an RAF Pilot on Anglesey at the end of next month. He was speaking at the Anglesey show on his first official engagement in Wales since returning here from paternity leave. He show goers by demonstrating his Welsh.
Prince William told the crowds at the Anglesey Show today that he and Kate will miss the area terribly when his posting comes to an end next month.
The duke was on his second official public appearance since the birth of Prince George.
He watched gundog and falconry displays, before meeting local young farmers in North Wales.
In a speech he said he was sorry Kate couldn't be there and joked that his son was "very good looking."
William in on a three-year tour as an RAF search and rescue helicopter pilot at RAF Valley in Anglesey which finishes at the end of September.
The Duke of Cambridge will visit the Anglesey show today. It's his second official public appearance since the birth Prince George.
He'll watch gun dog and falconry displays before meeting local young farmers at the 2 day event which attracts around 56 thousand people.
The television series that documents Prince William's time with the Search and Rescue operations coincides with the news that the service is to be taken away from the RAF and privatised - a move that the prince is believed to have opposed.
ITV News' Royal Editor Tim Ewart reports:
Prince William is to feature in a BBC documentary about the Search and Rescue service, where he has served as a Sea King pilot.
You can watch a preview of the documentary below:
BBC One Wales have released a short preview video for Helicopter Rescue, the documentary featuring Prince William and the Search and Rescue team at the prince's base at RAF Valley on Anglesey.
The Duke of Cambridge is shown piloting a helicopter on a rescue mission to a slate quarry in Blaenau Ffestiniog.
One of his crew are winched from the ground after rescuing a boy who had fallen off an old railway bridge onto rocks.
"As captain you're trying to play out the entire rescue, the transit to the rescue and back again in your mind, and pick up any circumstances or problems you can foresee, and try and fix them on the ground before you get airborne," he says in the programme.
Prince William is to be the subject of a BBC documentary series featuring his work as an RAF search and rescue helicopter pilot.
Helicopter Rescue will air on BBC One Wales in April, and will show the Duke of Cambridge serving with C Flight of 22 Squadron at RAF Valley on Anglesey since 2010.
Speaking in the documentary, he said:
"There's no greater feeling than when you've actually done some good and saved someone's life," he said.
"I don't think there's any greater calling in life… to be able to see a son or daughter's face when you bring their mother or father back from the edge of death - it's quite powerful."
Helicopter Rescue will air on BBC One Wales on Monday 8 April at 8:30 pm.**