Duke of Cambridge surprises runners at race in Sandringham on Father's Day

William, Prince George and Princess Charlotte gathering around a microphone and appearing to count down to the start of the race. Credit: PA

The Duke of Cambridge appeared at a running event in Sandringham with his two eldest children on Father's Day.

William surprised runners at a race around the Sandringham Estate on Sunday.

He will also turn 39 today, celebrating the final birthday of his 30s.

George and Charlotte were photographed wearing shorts and trainers, while the Duke was dressed in a blue shirt and a pair of navy chinos.

Brian Cook, who participated in the run and photographed the royal trio, said it was a "nice surprise, and nice of them to do"

According to the event's website, Run Sandringham was welcoming hundreds of runners of all abilities and ages to run a half marathon, 5K or community mile, with the aim of raising "many thousands of pounds for good causes".

It is understood the duke was not running in the event and was there in a private capacity.

The Cambridges also marked Father’s Day by posting a notice board style video featuring pictures of William with his father and brother from their younger days and a wedding photo of Kate and her father Michael Middleton.