Prince William with George and Charlotte at Sunday’s event. Pictures: Ian Burt

Surprised runners were given a royal countdown when they lined up for a new event on Sunday.

The Duke of Cambridge and his two eldest children Prince George, 7, and Princess Charlotte, 6, started the half-marathon runners off at the Run Sandringham event held on the royal estate. 

Prince William, who celebrated his 39th birthday on Monday, spent part of his Father’s Day supporting the participants.

Race director Aaron Murrell said the runners enjoyed seeing the Duke and family, who live at nearby Anmer.

An estimated 1,300 runners took part in the new event which also included a 5k and a community mile for all ages and abilities.

A number of charities benefitted from the Good Running Events day, including the organisers’ choices of the East Anglian Air Ambulance, Break and East Anglia’s Children’s Hospices, with runners also supporting their own causes. 

After the event, Sandringham Estate took to social media and said it was “sterling stuff from all the runners… despite the damp weather.”

Another event is planned around the estate on Sunday, September  26 which will be a fundraising 10k.

See the www.letsdothis.com website and search for Run Sandringham.