Unoccupied and unloved, its unkempt appearance is perhaps all the more surprising given that the person who bought it can now be revealed as one of the richest men in his mineral-rich homeland of Kazakhstan.
Timur Kulibayev, the son-in-law of the Kazakh president and worth an estimated £1.7 billion in 2008, admitted this weekend that he is the owner of the Ascot mansion. He bought it from Andrew for £3m above the asking price, even though there were no other bidders.
His admission comes after nearly three years of secrecy over the building's ownership. Kulibayev only acknowledged his role after The Sunday Times painstakingly unravelled the chain of offshore companies he had used to obscure the 2007 purchase.
Insiders say Kulibayev's decision to pay over the odds for Sunninghill may have been an attempt to win Andrew's friendship.
Last night fresh questions were being raised over Andrew's judgment in accepting the money from a businessman now subject to claims of financial impropriety in his homeland.
Ian Davidson, a Labour member of the Commons public accounts committee, questioned whether the prince was "blinded by the opportunity to make a windfall profit".
"Possibly the work he does in Kazakhstan is to the benefit of Britain," said Davidson. "But he has got to avoid giving the impression that he is for sale or at least for rent."
Kulibayev, 43, who is married to Dinara, daughter of President Nursultan Nazarbayev, made his fortune from natural resources in Kazakhstan, which has some of the world's richest gas and mineral reserves.
However, he has frequently been criticised for removing wealth from his homeland, and is currently embroiled in a row involving tit-for-tat corruption allegations with a group of exiled opponents in Britain. Members of his family have also been subject to an abortive investigation in Liechtenstein into money laundering.
Kulibayev has left the 12-bedroom Sunninghill, a wedding present from the Queen to the Duke and Duchess of York, unoccupied, and it has fallen into decay — the latest stage in a sometimes ill-starred history.
The house's style was widely derided as "supermarket". Andrew and Sarah were divorced in 1996, but continued to live at Sunninghill with their children Beatrice and Eugenie. The duke eventually moved out in 2004, two years after the house had been put up for sale.
It languished on the market, valued at £12m, until it was suddenly bought in 2007. The high price came even though there were no other bidders.
The buyer was named in the Land Registry as Unity Assets Corporation, based in the British Virgin Islands (BVI). Although The Sunday Times in 2008 identified Kulibayev as the probable buyer, this could not be established for certain.
Contracts on Sunninghill were exchanged in June 2007 and the deal was completed in September in a sale signed off by Mark Bridges, a solicitor at Farrer, the firm which represents the Queen, and by Sir Alan Reid, the monarch's keeper of the privy purse.
Leaked corporate documents from the BVI and from Kazakhstan, seen by The Sunday Times, unravel the link from Unity to Kulibayev. Share registers show Unity is owned by Merix International Ventures. Merix is owned in turn by Kipros Ltd, also registered in the BVI.
At the time of the purchase, Kipros was owned by Kipros limited liability partnership, registered in Almaty, the former capital of Kazakhstan. Kazakh registration documents from 2007 show Kulibayev as controlling the partnership, and in 2008 its sole share in Kipros Ltd was transferred to him personally.
Further documents show Sunninghill was just one of Kulibayev's British purchases. Also in 2007, he paid a total of £44.4m for four adjoining houses in Upper Grosvenor Street and Reeves Mews in Mayfair. They were bought in the names of Merix, Vitala and Lynn, all Kulibayev companies.
At the time, both Kulibayev and the palace refused to discuss the Sunninghill purchase. As recently as last Friday morning, Kulibayev denied he was the owner of the properties.
"I am not the owner and I don't know why you are asking me these questions," he said to a reporter. However, when he was then read the names of the BVI companies he declined to comment further, referring questions to "my people".
His London solicitors Magwells later answered on his behalf. Their response said: "Sunninghill was purchased by and is still owned by companies that are legally owned by Mr Kulibayev." The lawyers also confirmed that the London properties were owned by Kulibayev's companies.
A source close to the negotiations suggested that the inflated price was prompted by Kulibayev's hope of doing the prince a favour and so buying a sense of obligation from him.
The prince might then be more willing to accept invitations to meet Kulibayev, polishing the tycoon's image as an international businessman taken seriously by the British royal family. Kulibayev's lawyer, however, insisted the decision to pay over the asking price had been purely "a commercial decision".
Despite Kulibayev's new openness, Buckingham Palace was still refusing to discuss the Sunninghill deal this weekend, describing it as "private" and insisting there had been "no impropriety" involved.
A spokeswoman confirmed the prince had visited Kazakhstan officially in 2003, 2006 and October 2007. However, it is known he has made "private" trips to Kazakhstan in the past few years, and Kulibayev confirmed this weekend he had met Andrew "several times" since the Sunninghill purchase.
Andrew has also been linked to Kulibayev's circle through Goga Ashkenazi, a Kazakh-born businesswoman based in London. She is a former mistress of the tycoon and played a key role in the Sunninghill deal. In June 2007, Andrew presented her to the Queen at Royal Ascot, barely a mile from Sunninghill, days after the exchange of contracts for the property.
Six months later, Ashkenazi gave birth to Kulibayev's son at the Portland hospital, London.
Andrew's friendship with the Kazakhs continues. Last weekend, he was a guest at Ashkenazi's 30th birthday party at a country house in Buckinghamshire.
Other guests included the steel tycoon Lakshmi Mittal, who has multi-billion-dollar investments in Kazakhstan. Documents from 2008 show Merix, one of the firms linked to the Sunninghill purchase, had borrowed $795m (£507m) from a Mittal company.
The new revelations come at a difficult time for Kulibayev. As President Nazarbayev's son-in-law, he has long been considered the second most powerful man in the former Soviet republic and as heir apparent.
In 2007, however, he fell out for a while with Nazarbayev and was fired from one of his main state industry jobs — perhaps partly because of Ashkenazi's pregnancy. He is widely believed to have been looking at the time for new destinations for his money outside Kazakhstan.
Questions have long been raised about exactly how Kulibayev accumulated his fortune, estimated at £1.7 billion two years ago by Forbes magazine. Much of his working life has been taken up with public roles, such as running KazMunaiGaz, the state oil and gas body. The pay for such positions is slight compared with his fortune, which includes a large stake in the Kazakh bank Halyk, held jointly with his wife Dinara.
Last month, a series of allegations were aired against Kulibayev in Kazakhstan that have prompted an investigation into him by the country's financial police. Mukhtar Ablyazov, former head of BTA, the largest Kazakh bank, accused Kulibayev of acting corruptly in 2003 and garnering hundreds of millions of dollars.
Kulibayev, who denies all the allegations, reacted explosively, successfully applying to a court to stop the print runs of three Kazakh newspapers publishing the allegations.
After an international outcry, the Kazakh court reversed its decision and the police launched their inquiry.
Ablyazov, who lives in London, is accused by the current management of BTA of irregularities in his time at the bank and is facing a High Court action, which he is fighting.
Ablyazov said: "The multi-million spree, and the attempts to conceal this by Mr Kulibayev, raise questions about how he makes his living."
Kulibayev has never lived in his UK homes and they are now empty. It is thought Sunninghill has become such a millstone for Kulibayev that he is keen to sell it. When the suggestion was put to him through his lawyers on Friday he did not deny it.
Kulibayev's Mayfair properties are looking similarly forlorn. The houses in Upper Grosvenor Street, five-storey buildings with Edwardian facades, have boarded-up basement windows and metal grilles over the doors.
Some may consider this a shocking waste of valuable housing. Kulibayev's lawyers, however, described them, perhaps optimistically, as "assets in various stages of refurbishment".
Who's who
Nursultan Nazarbayev, president of Kazakhstan
Timur Kulibayev, billionaire son-in-law of Nazarbayev
Dinara Kulibayeva, daughter of Nazarbayev, wife of Kulibayev
Goga Ashkenazi, friend of Prince Andrew and ex-mistress of Kulibayev
Mukhtar Ablyazov, former banker, political opponent of Kulibayev
The Sunday Times
