Prince George and Princess Charlotte, looking on from a boat with their grandparents, Carole and Michael Middleton, cheered as their parents went head to head in a sailing event off the Isle of Wight.
It was the latest instalment in a long-running rivalry for the Prince and his wife.
In 2011 the Duke trounced the Duchess in a competitive dragon boat race in Canada.
Not to be outdone, the Duchess got her revenge three years later when she won a sailing event in Auckland during their tour of New Zealand.
The Prince then reclaimed victory in 2017 in a riverboat race against his wife in the German city of Heidelberg.
So it was that the stakes were high at yesterday’s King's Cup regatta, an event the royal power couple announced in May and hope will become an annual event to increase awareness of the benefits of sport and to raise support and funds for worthy causes.
Ever the philanthropists, each yacht in the race represents causes supported by the Duke and Duchess.
Yesterday the HRH sailed for Child Bereavement UK while the Duchess competed on behalf of The Royal Foundation.
Doubtless we would have all loved to see the Duchess even the score, however a royal win was not to be with celebrity adventurer Bear Grylls beating both the royal couples’ teams to the finish line.
The Duke tied third while the Duchess was handed a giant wooden spoon for coming last in the sailing spectacle.