A diamond and sapphire brooch that belonged to Princess Margaret will be sold at Woolley and Wallis in Salisbury on April 28.
The lot is valued at around £12,000-18,000 ahead of the auction.
The bow shaped piece is mounted in platinum and gold and dates to 1920s. While the exact date that the princess acquired it is unknown, she was first seen wearing it in 1948.
Jonathan Edwards, a spokesman for the auction house, told the Daily Mail: "Princess Margaret loved jewellery and she had the most wonderful collection.
"This brooch is a beautiful thing and it's an interesting piece itself - in between Edwardian and Art Deco - but it's Princess Margaret that makes it valuable.
"If it came over the counter it would probably be worth about £4,000, it has four times that value because of its connection to the princess and its incredible provenance.
"It's stamped on the back with her cipher, all her jewellery was stamped in this way. It's a little script M with her coronet on top of it."
Princess Margaret (1930-2002) was a glamorous figure whose love of jewellery was well known.
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