A 1964 Ferrari 330GT is expected to make more than half a million pounds in a charity auction for Prince William's employer, the East Anglian Air Ambulance.
The specially commissioned Nembo Spyder - with a 4 litre V12 - was owned by motor enthusiast and collector Richard Allen until he died on November 26.
He left the car to be to be auctioned off in memory of the time the ambulance came to the help of one of his fellow racing drivers after a crash.
Previous auctions of the same car have seen sales of £660,000.
Mr Allen, from Essex, bought the car from Italy in the mid-nineties and decided not to drive it on the road but display it regularly at Ferrari events in the UK.
It is to be sold at auction by H&H Classics to benefit the EAAA on March 29 at the Imperial War Museum, Duxford.
Richard Allen, was chairman of the UK's Ferrari Owners' Club for many years.