The Duchess of Cambridge indulged her passion for sailing when she joined Sir Ben Ainslie as he launched Britain's bid to win the America's Cup.
The Olympic gold medal winning sailor will skipper the team that aims to win the historic trophy - something a British team has never done.
Kate, who wore a Jaeger dress, has been a keen sailor since childhood and even raced and comprehensively beat William in Auckland earlier this year - in yachts used by New Zealand in the America's Cup.
The Duchess' support for the team will be a long-term commitment and will see her "getting out there" to back the challenge, said a Kensington Palace spokeswoman.
Sir Ben was famously employed as a tactician during the last America's Cup race, helping the US Oracle team overturn an 8-1 deficit to beat New Zealand.
The sportsman, who is the most successful Olympic sailor of all time with four golds and a silver, said he had a burning desire since he was a child to be part of a British America's Cup bid.
The Olympic sailor said: "We want to bring it home, it would be an amazing thing for this country."
Sir Ben added: "I had this burning desire and ambition to be part of a winning America's Cup team and ultimately a winning British America's Cup team and so was very fortunate to be involved with Oracle last time.
"That was a fantastic experience a great team, we have a lot of respect for them, for team New Zealand, all of the other competitors - but we want to win this for Britain."
He will skipper the team that aims to triumph in the 35th America's Cup being staged in 2017, with the entry made through the Royal Yacht Squadron club.
The Royal Yacht Squadron club hosted the first race which took place off the Isle of Wight in the mid-19th century.
Former Channel 4 boss Lord Grade said of Kate: "She's a keen sailor, she loves her sailing clearly, you can just tell. You can see it in her eyes. It's great for everybody she's got behind it and supporting it."
Lord Grade, a board member of Britain's bid to win the America's Cup added: "We've got the best chance we've ever, ever had. It's not going to be easy, but I don't think Ben would risk his reputation if he didn't believe we had a real chance of winning."
In his speech at a private reception for team members and sponsors held at Queen's House in Greenwich, he said, with the trophy nearby: "At 163 years old, the America's Cup here is the oldest trophy in world sport and Britain has never won it.
"The first race was organised by the Royal Yacht Squadron and was around the Isle of Wight. It was open to yachts of all nations and 18 were entered. In 1851 America won this nascent contest for maritime supremacy, outclassing the rest of the field to be the first at the finishing line at Cowes - of course.
"The black schooner won a 4ft high trophy called the Hundred Pound Cup and to honour that victory it was renamed the America's Cup and became a challenge trophy."
Sir Keith Mills, also a board member, said Sir Ben had offered to take Prince George out on the water when he is old enough, and Kate readily agreed.
Sir Keith, who was deputy chairman of the London 2012 organising committee, said of the Duchess: "We were all sharing sailing stories and sailing is in her family."
He added that they would be inviting Kate to watch the 2017 race - whose US course has yet to be announced.
Later at a press conference to officially launch Britain's bid to win the race, he said: "The most important thing about today's announcement is to get the whole of this country behind the Ben Ainslie racing team.
"Without the support of the whole country we aren't going to be able to attract the commercial sponsors that we need and we know that Ben has a huge following out there.
"So the Duchess has lent her support to the team to help us raise the awareness of what we're doing, and over the next few months we hope she will be involved in some very specific things."
Before leaving, Kate posed with Sir Ben and leading members of the bid team alongside the America's Cup.
In the background was an America's Cup 45 class twin hull vessel, which will be used for training and racing up until the event starts, when another class of yacht will be used.
Professional yachtsman Freddy Carr, who is part of the Olympic sailor's crew, praised Kate's sailing abilities.
He said: "She was down in New Zealand in Auckland, sailing with their team on the New Zealand America's Cup yachts, and did very well.
"If Ben's not up to the job, we'll get Kate."