Wallis Simpson, an American divorcee who won the heart of the future King Edward VIII, is believed to have travelled around London in secret with her beau in a 1933 Humber Snipe.
The car is set to go under the hammer at Bishton Hall in Staffordshire, Hansons Auctioneers' country house saleroom, tomorrow, together with 15 other vintage Humbers.
The Wallis Simpson-linked motor has a guide price of £20,000-to-£40,000.
The cars had meant to go under the hammer earlier this year.
Alan Marshall, aged 64, from Hull, is auctioning off his remarkable motors, gathered over 60 years first by his father Reg and then by him, because of spiralling maintenance and storage costs.
He said: "I was told the car had been used by Edward and Mrs Simpson because it was perfect for privacy.
"Thanks to its small back window you couldn’t see who was inside.”
Wallis and the future King Edward first met at a fox-hunting weekend in 1931.
By 1934, they were lovers and Prince Edward was said to be besotted by her.
Edward's relationship with the twice-divorced American led to grave concerns in British Government and the couple were followed by the Metropolitan Police Special Branch.
When King George V died in 1936, Edward ascended the throne – but his reign was short.
His plan to marry Wallis caused a constitutional crisis that led to his abdication that same year.
Rik Alexander, manager of the Humbers sale on behalf of Hansons, said: “If Special Branch followed Edward and Mrs Simpson around, the Humber would have certainly suited their needs.
"A place to hide from prying eyes. I think buyers will be intrigued by this car’s romantic royal connection and place in history.
'Roll their sleeves up'
“But the successful bidder will have to roll their sleeves up. They won’t be able to drive the car straight away.
"It’s a restoration project and needs its engine re-installing.”
For more information about the auction, visit the Hansons website.