The beautiful ornamental crown fetched more than double its estimate more than a hundred years after it was given to Lady Delia Spencer by the sixth Earl Spencer in 1914.
The breathtaking tiara is set with more than eight hundred diamonds and held on its frame by tiny and beautifully engineered wing-topped screws, so that it may be removed.
When divided by the hidden clasps the central three sections become a choker necklace and the two outer sections form a bracelet.
Known for its superb craftsmanship it was given to Lady Delia on her wedding by the Hon. Sidney Peel who was the younger son of Lord Peel the Prime Minister.
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Lady Delia's father had six children. His son, Albert Spencer died when his granddaughter, Diana was just 14.
Diana went on to marry HRH Prince Charles and her brother, also called Charles, took the Earldom in 1992.
At the time it was heralded by the nation's press including The Times which gave an extensive report of the wedding and mentioned the Earl's gift to his daughter.
Lady Delia was described by her niece as: "There are very few life enhancers in this world and Delia was definitely one.
"Anybody who came into contact with her was the happier."
The tiara was only expected to raise £30,000-£40,000 but bested its lowest estimates by £40,000 at the Cheffins November Fine Art sale in Cambridge on Wednesday.