A watch hidden inside a gold coin which King Edward VIII gave his first mistress as a secret love token is expected to make more than £15,000 at auction next week.
The young Prince of Wales began a passionate affair with married socialite Freda Dudley Ward in 1918 after they met in a doorway in London's Mayfair as they sheltered from a Zeppelin raid.
But he broke off the relationship in 1934 when Wallis Simpson came into his life - and sparked the dramatic abdication crisis.
Prince Edward was presented with the wafer-thin watch, created inside the 1902 £5 gold coin, when he opened the Scottish Motor Exhibition in 1927 and had it engraved with the initials 'F' and 'D', for his pet name David, and presented it to his secret lover.
Auctioneer James Grinter said: "This watch is a unique piece of royal history linked to the man who became the Duke of Windsor and we are expecting a lot of interest from collectors around the world."
The watch is due to go under the hammer on 19 June in Colchester auctioneers Reeman Dansie's sale of Royal memorabilia which includes items from the Queen, Princess Diana, the Queen Mother, the Duke and Duchess of Windsor and other monarchs.
It is estimated at £10,000 to £15,000.
Mr Grinter said: "The watch has a beautifully-made, extremely thin 18-jewel movement by Stablis of Switzerland so it can actually be closed on a hinge inside the £5 coin.
"The Prince was obviously impressed by the concept because he later bought a very similar £5 gold coin watch from Cartier for Wallis Simpson and that sold two years ago at Sotheby's for £27,500."
The Prince of Wales and Freda Dudley Ward were both 23 when they met in 1918 and began their affair. She had already been married for five years and had two daughters by a husband 16 years her senior, but that didn't stop the Prince bombarding her with extravagant gifts - including the watch.
Next week's Royal sale also includes a rare dinner menu from the Canadian steamship RMS Lady Somers signed by the Duke of Windsor and Wallis Simpson as they sailed to the Bahamas in August 1940, where the Duke was due to take up his post as Governor.
The signed menu, which is estimated at £250 to £350, shows the couple dined on dishes including Canapes de Langouste Rossini and Roast Quarters of Lamb a la Menthe.
Reeman Dansie's Royal memorabilia sale is in Colchester on 19 June.