Princess Diana's Audi goes on sale A 1994 Audi Quattro convertible once owned by Diana, Princess of Wales will be one of the star lots at an auction at Blenheim Palace on June 29. The Audi was the family car in which Diana, Princess of Wales was photographed in a number of occasions driving Their Royal Highnesses Prince William and Prince Harry in 1994. Until the auction, the 2.5-litre-engined car is on display at the Grange St. Paul's Hotel in London. Chris Routledge, the managing director of Coys, which is staging the auction at Blenheim Palace, said: "This is an extraordinary opportunity to own a piece of royal history. We have put a guide price on the car of between £20,000 and £25,000 but we have no idea what it will go for. Although we had not formally released the fact that the car was for sale until now, we have already had enquiries from around the world and particularly from America. The car is in immaculate condition and has only 21,000 miles on the clock. Visitors to the hotel will be able to leave a sealed bid for the vehicle, which will then be given to the auctioneer at Blenheim. Coys and Grange Hotels are also planning a competition where the winner will be driven in the car at Blenheim, entertained to lunch and will then attend the auction.