A Ford Escort which was given to Diana, Princess of Wales by the Prince of Wales as an engagement present is up for auction after the current owner kept the car’s origins a secret for 20 years.

Lady Diana Spencer received the 1981 silver 1.6L Ghia saloon from Charles two months before they were married.

She often drove it to watch the prince play polo, and the bonnet features a silver frog – a copy of the original mascot which was given to the princess by her sister Sarah and which Diana kept when she sold the car.

The princess stopped using the vehicle soon after giving birth to Prince William in 1982, and it was later bought for £6,000 by an antiques dealer.

It eventually ended up, in around 2000, with its current owner – a royal fan who kept it for decades and drove it only sparingly without disclosing its history to her friends.

Lewis Rabett, of the Reeman Dansie auction house in Colchester, Essex, said the car had disappeared from public view for more than 20 years.

“The lady who owns it kept it in classic car storage but it used to be in her garage at home and when friends came round and saw it she would just say: ‘That’s my first car’,” Mr Rabett said

“She was very coy about whose it was and I think obviously quite liked having the knowledge of it being special.

“She kept it a secret. Her family knew, but not her friends. She liked and respected the things Diana achieved in her lifetime.”

The immaculate vehicle still carries its original registration WEV 297W, and has 83,000 miles on the clock as well as its original paint and upholstery.

It is expected to fetch between £30,000 and £40,000 at Reeman Dansie’s Royal Auction on June 29 – one month ahead of the 40th anniversary of Charles and Diana’s wedding day.

Mr Rabett said the forthcoming sale had attracted a great deal of inquiries, particularly from the US.

“Diana was obviously very revered in the States, and the Duke and Duchess of Sussex’s recent birth has brought Diana’s name back into people’s attention again.”

Harry and Meghan named their newborn daughter, who arrived on Friday, Lilibet ‘Lili’ Diana, paying tribute to both the Queen and Harry’s late mother.