It had belonged to a royal fan since about 2000 who drove it sparingly without revealing its story to friends.
The vehicle was sold to a telephone bidder in an online auction by Reeman Dansie of Colchester, Essex, for £ 52,640 on Tuesday.
The hammer price was £ 47,000, exceeding the pre-auction estimate of £ 30,000 to £ 40,000.
The car still has its original registration, WEV 297W, as well as its original paint and upholstery, and has 83,000 miles on the clock.
Lewis Rabett of Reeman Dansie Auctions in Colchester, Essex, said the bid came from a museum in Chile, South America, and the car would be shipped there.
“The interest was considerable before the auction,” he said.
“Landing in South America is proof of the global interest in the car.
“It is also evidence of Diana and her enduring legacy.”
Diana, Princess of Wales, was very popular in Chile and in 2010 the Museo de la Moda in Santiago paid £ 192,000 for one of her first official dresses.
The museum said at the time that it was ready to pay the princely sum because it was an important piece of fashion history.
The Duke of Sussex and the Duke of Cambridge will meet on Thursday 1st July to unveil a statue in memory of their mother Diana, Princess of Wales, in the sunken garden of Kensington Palace.