Prince George and Princess Charlotte looked on as their parents were denied victory at the King’s Cup yachting regatta by adventurer Bear Grylls.
The Duke and Duchess of Cambridge went head-to-head in the event off the Isle of Wight a day earlier than planned due to forecast bad weather on Friday.
George and Charlotte joined their grandparents Carole and Michael Middleton on a boat to watch the sailing spectacle.
William and Kate competed against each other, and a host of celebrities, including comedian John Bishop, on a cloudy but relatively calm day around Cowes.
The dull weather did not stop the couple sporting shorts for the two races, but a royal win was not to be, with Grylls winning overall.
William finished third and Kate finished seventh in the first race.
Ahead of the first race, the boats were recalled to the starting line after an initial false start in which some of them were over the line.
And in the second race, many boats – including Kate’s – were disqualified for not going back and starting the race at the line.
The duchess, wearing a baseball cap with her hair in a ponytail, sat on the side of her boat alongside crew members for the afternoon of sailing.
Heavy rain has been forecast for much of the country on Friday, with strong winds also expected, especially in the south, which could have proved a problem for the sailors taking part in the event.
The yachts represented causes supported by William and Kate.
The duke was competing on behalf of Child Bereavement UK, England Women’s footballer Fara Williams represented Centrepoint, television presenter Dan Snow raced for London’s Air Ambulance Charity’s 30th anniversary campaign, and Grylls was skipper on a yacht for wildlife conservation organisation Tusk.
Kate chose four of her patronages and was competing on behalf of the Royal Foundation, in connection with her work on the early years development of children.
Bishop was competing for Action on Addiction, BBC presenter Katie Thistleton was supporting Place2Be, and Olympic champion rower Helen Glover was taking part for the Anna Freud National Centre for Children and Families.
The winning team will be awarded the King’s Cup, a trophy first presented by King George V at Cowes’ Royal Yacht Squadron in 1920.
William and Kate hope the King’s Cup regatta will become an annual event, increasing awareness of the benefits of sport, while also raising support and funds for their causes.
The event gave the couple the chance to renew their sporting rivalry.
The duke trounced his wife when they competed in a dragon boat race in Canada in 2011, but Kate got her revenge three years later when she won a sailing event in Auckland during their tour of New Zealand.
William took the honours again during a visit to the German city of Heidelberg in 2017 when he was victorious in a riverboat race against his wife.
Members of the public watched the race from the SailGP Race Village along the Cowes foreshore.