Prince William has been forced to cut off one of his charity donors after she allegedly tried to sell access to him for £20,000. Minerva Mondejar Steiner, a Filipina-Swiss millionaire, owns an art gallery that was an official sponsor of William's annual charitable polo event, before it was discovered she had allegedly offered people private meetings with the prince for cash - something William, 43, was reportedly unaware of.

In a "strictly private" email seen by The Times, Mondejar Steiner, who had been invited to the match, allegedly invited wealthy individuals belonging to a luxury concierge service to the polo match, where she said in exchange for donations to her own philanthropic foundation, they could attend the event or join her in meeting William.

The email read: "As a patron of the Mondejar Foundation, you are invited to support their philanthropic work through a charitable donation, in return for which you will be welcomed to this prestigious occasion. Patron contributions: £6,000 - admission for one patron. £20,000 - includes full access plus a private audience with Prince William and Princess Catherine."

Those who received the email, including members of the Swiss company A Small World, were also told that the invite should not be "shared publicly."

In another document seen by The Times, Mondejar Steiner's team offered potential advertisers the opportunity to meet William.

Potential advertisers were told that for £50,000, they could have a double-page editorial spread in a magazine handed out at the event attended by millionaires, along with two "VIP tickets", which would give them seats and "access to the royals".

A Kensington Palace source said William did not "condone" the behaviour.

The palace also said it had no idea Mondejar Steiner was using the occasion to raise money for her own causes or promising access to William for cash, which would not be the case.

It is believed the Palace was only familiar with Mondejar Steiner's gallery and not her foundation and did not know she was using the event to raise money for her own rather than William's project.

Mondejar Steiner is no longer allowed to sponsor the event, which runs on an invitation-only basis. The Royal Charity Polo Cup match takes place annually, and millionaire donors gather to watch Prince William play polo. These donors then donate money to causes close to the future King's heart, with the event last year raising £1 million for charity.

The Times said the Palace declined to say how much Mondejar Steiner had paid to become a sponsor for the event or put on her own art exhibition at the match.

The Daily Express has contacted Kensington Palace for comment.