The lady, who owned the SL500 sports car parked it in a garage in Knightsbridge, central London, having driven it just 75 miles before she managed to lose the keys to her birthday present.
Instead of getting a replacement, she decided to never drive it resulting in a 21 year old car in a brand new condition.
The car is expected to sell for more than £55,000 on Wednesday when it is auctioned by Coys at the Royal Horticultural Society in London.
This is around TEN TIMES the price of a normal SL500 of the same age.
The car now has a set of keys and is being sold with a letter from the lady’s butler verifying its mileage and provenance.
Chris Routledge, CEO of Coys, said: “This is a car with a fantastic story. Purchased as a birthday present and driven only 80 miles before the owner lost the keys and never drove it again.
“It even comes with a letter written by the owner’s butler verifying its mileage and its provenance.”
Mr Routledge added:
“Had she not lost the keys and used it regularly, we estimate it would now be worth between £5,000 and £7,000, but the fact that it has kept such a low mileage and has not been driven in more than 20 years makes it worth between £45,000 and £55,000.
“What happened with the keys remains a mystery but the car comes with new keys for the new owner.”