The allegation from Goga Ashkenazi, who has been romantically linked with the prince, contradicts Buckingham Palace's assertion that he had kept out of the deal
She says she introduced Andrew to the buyer, Timur Kulibayev, her lover and son in law of Kazakhstan's president.
He paid £15million for the 12-bedroom Sunninghill Park in Berkshire in 2007 - even though it had been languishing on the market for more than five years.
Prince Andrew was involved in the controversial sale of his former home to an oil tycoon for £3 million more than the market price, it is claimed
Miss Ashkenazi described it as a property deal between friends. 'A deal was struck and the asking price was paid,' she added.
The glamorous businesswoman's claims will prove extremely embarrassing for palace aides, who have always rejected suggestions the prince acted improperly.
Andrew's spokesman maintains the sale was a 'straightforward commercial transaction' conducted on the prince's behalf by a trust headed by the Queen's financial adviser and her lawyers.
The palace has tried to distance him from the property deal because of his official links with Kazakhstan as a UK trade envoy.
Andrew has enjoyed hunting trips with president Nursultan Nazarbayev, who has been accused of corruption and vote-rigging.
Miss Ashkenazi, who is the mother of Mr Kulibayev's love- child, Adam, made her claims in a 17-page spread in Hello!.
One photograph shows her with the prince in the royal box at Ascot in 2007 when he introduced her to the Queen. The exchange of contracts for Sunninghill took place days later.
Asked about her role in the sale of Sunninghill to Mr Kulibayev, she answered: 'I merely made the introduction and the rest was left to the two of them.
'Ultimately, it was like any property deal between friends. A deal was struck and the asking price was paid.'
To emphasise her closeness to Andrew, Miss Ashkenazi spoke in the magazine about her appearance at two parties to celebrate the prince's 50th birthday earlier this year, one hosted by the Queen at Buckingham Palace and the other hosted by his two daughters at St James's Palace. She described the Queen as friendly.
Sunninghill was given to the prince by the Queen as a wedding present on his marriage to Sarah Ferguson in 1986. It was where the couple, who divorced ten years later, brought up their two daughters.
Andrew moved out in 2004, two years after the house had been put up for sale.
It languished on the market valued at £12million until it was suddenly bought in 2007 by a mysterious trust based in the British Virgin Islands which, it subsequently emerged, was linked to Mr Kulibayev.
Since then questions have been raised about his motivation for buying the property, with repeated suggestions that he hoped to ingratiate himself with the prince in the hope of securing favours and boosting his public profile.
This was heightened by the Mail's revelation that the mansion hasn't been lived in since the sale. It has since fallen prey to vandals.
Last night a Buckingham Palace spokesman declined to comment on the latest revelations saying: 'This was a private sale and we would not comment on any aspect of the sale.'
A royal source denied there had been any impropriety about the property deal, adding: 'To suggest that the Duke of York has benefited from his public work in Kazakhstan is utterly untrue.'
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