Prince William, George and Charlotte start races at Sandringham

The prince and his two children counted down from 10 to start three races in the first-ever Run Sandringham event.

Prince William, Duke of Cambridge with Prince George and Princess Charlotte arrive to officially start the half marathon on the Sandringham Estate (Image: Ian Burt Photography)

William, George and Charlotte arrived just before the half marathon got under way. They walked to the stage holding hands, before sending runners on their way.

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They Royals' arrival was a secret known only to race organisers beforehand. The trio are believed to be staying at nearby Anmer Hall.

The Royal trio waved at runners and shouted encouragement as they set off from the starting line (Image: Ian Burt Photography)

Surprised participants took selfies of William, George and Charlotte, who waved, clapped and shouted encouragement as runners set off from the starting line on three different routes through the pine woods and the lanes.

Prince William was dressed casually, in an open-necked shirt and jeans, while both George, aged seven and six-year-old Charlotte wore shorts.

Prince William encourages the runners on at Run Sandringham (Image: Ian Burt Photography)

Neither the Duchess of Cambridge or Prince Louis, aged three were seen at the event, which was taking part for the first time on the Queen's Norfolk estate.

Runners could choose between a half marathon, 5k or community mile, with many raising funds for charity including King's Lynn-based Scotty's Little Soldiers, which support the children of fallen servicemen and women.

The start of the half marathon at Run Sandringham (Image: Ian Burt Photography)

Event organisers said it was "a major new event in the East Anglian running calendar", which would "attract a large field of runners of all abilities to the Winter Residence of Her Majesty the Queen, to run around the Sandringham Estate and surrounding roads and trails, while raising thousands of pounds for good causes".

They added: "With a start and finish within the Sandringham Estate, including passing directly in-front of Sandringham House, the event boasts a scenic route with stunning views of the Norfolk countryside."

Hundreds took part in Run Sandringham, where Prince William, Prince George and Princess Charlotte counted them down to start (Image: Ian Burt Photography)

Their website said tributes to the "huge army of volunteers"who would make the event possible.

It went on: "Volunteering is extremely rewarding and you don’t need any previous experience to take part."

Prince William, Duke of Cambridge with Prince George and Princess Charlotte, who clearly enjoyed joining the volunteers helping out at Run Sandringham (Image: Ian Burt Photography)