The fundraising event is being held again today.
The Prince of Wales is set to take part but his wife — who is being treated for cancer — will not be joining him.
Last year, William was on the winning team at the Royal Charity Polo Cup, held at Guards Polo Club in Windsor, Berks.
And Kate was on hand to present her husband with the trophy.
The day raised £1million for “well-deserving causes the Prince and Princess are passionate about”.
It will be the 13th time William has played in the event, which has made a total of £13million.
Wales Air Ambulance, of which William is patron, was among the beneficiaries last year, getting a cheque for £115,000.
Chief executive Dr Sue Barnes said: “We are one of the newest patronages of HRH The Prince of Wales and it was humbling to be one of the charities chosen to benefit from this event.
“The Prince takes a keen and proactive interest in our charity and, as a former air ambulance pilot, understands better than most the importance of such a service.
“He has become a passionate member of the Wales Air Ambulance family.
“We are overwhelmed to be chosen as a beneficiary of the Polo Cup again this year.”
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Mountain Rescue England and Wales, visited by the royal couple last year, has also received much-needed money from the event.
Other charities getting cash this year include the Motor Neurone Disease Association.
Earlier this year, Wills handed CBEs to MND charity heroes Rob Burrow, who died in June aged 41, and his best pal Kevin Sinfield.
Yesterday, Prince William was in Lambeth, South London, to mark the first year of his Homewards initiative to tackle homelessness.
