The Duke and Duchess of Cambridge are going head to head in the King’s Cup yachting regatta.
William and Kate are taking part in the event off the Isle of Wight a day earlier than planned due to forecast bad weather on Friday.
The couple are competing against a host of celebrities, including comedian John Bishop and adventurer Bear Grylls, on a cloudy but relatively calm day around Cowes.
Kate and William are sporting shorts for the event, and could be seen getting in some last-minute training ahead of the race which started after 2.30pm, 30 minutes later than scheduled.
The boats were recalled to the starting line after an initial false start in which some of them were over the line.
The duchess, wearing a baseball cap with her hair in a ponytail, could be seen sitting on the side of her boat alongside crew members.
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 represent causes supported by William and Kate and are racing in the waters around Cowes.
The duke is competing on behalf of Child Bereavement UK, England Women’s footballer Fara Williams represents Centrepoint, television presenter Dan Snow is racing for London’s Air Ambulance Charity’s 30th anniversary campaign, and Grylls is skipper on a yacht for wildlife conservation organisation Tusk.
Kate has chosen four of her patronages and is competing on behalf of the Royal Foundation, in connection with her work on the early years development of children.
Bishop is competing for Action on Addiction, BBC presenter Katie Thistleton is supporting Place2Be, and Olympic champion rower Helen Glover is 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 is also giving 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 can watch the race from the SailGP Race Village along the Cowes foreshore, which is free to access and includes an 800-seat grandstand.
Footage from the race will play on screens across the town and there will be a number of family-friendly activities and exhibits to promote sailing around the event, including initiatives and programmes for children and young people.