Sotheby's says Marie Antoinette, who was executed by guillotine during the French Revolution, was often portrayed wearing pearls.
The auction house says they were as prized as diamonds in the late 18th century.
Now, dazzling diamonds and natural pearls once worn by the French Queen are being shown in London, ahead of an auction in Geneva on November 14.
King Louis XIV and his wife Marie Antoinette lived in the decadent Palace of Versailles before the French Revolution of 1789 forced them to Paris.
Sotheby's jewellery specialist Benoit Repellin says Marie Antoinette smuggled her treasured collection abroad as revolution consumed France.
"She indeed packed her jewellery, her pearls and diamonds before planning to escape to Varennes," he says.
"So, she sent her jewels and pearls to Vienna and to Brussels first where her sister Maria Christina was governor.
"And she asked the Count Mercy Argentua to send all of her jewels to Vienna, so to her family because she was born Archduchess of Austria, she was the daughter of Empress Maria Theresa.
"So, all the jewels were then delivered to the imperial palace in Vienna to be kept until the end of the French Revolution."
Marie Antoinette died at the guillotine at the age of 37 in 1793.
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Her collection eventually found its way to Louise of France, Duchess of Parma and grand-daughter of Charles X, King of France.
She in turn left it to her son, Robert I, the last ruling Duke of Parma. The collection stayed in the family till now.
"I think this is a once in a lifetime opportunity to buy Marie Antoinette's jewellery," says Andrew White Correal, senior director of jewellery at Sotheby's.
"It hardly ever comes anything from her to the market and, in this case actually, it's the first time in 240 years that people are going to be able to buy them.
"They have been inherited since her death, so it's unique, absolutely unique."
Sotheby's says the highlight of the collection, 'Queen Marie Antoinette's Pearl' - a diamond and pearl brooch - is expected to fetch up to US$2 million.
"It's like a huge drop-shaped natural pearl, measuring 25.85mm length," explains Mr Repellin. "So, it's even larger than the Peregrina, which was part of the collection of Elizabeth Taylor.
"So, it's a very important item by the size of the pearl and the quality of the pearl, but also with all the history behind it, coming from the most famous queen of the world, probably."
One of these monogrammed rings contains a lock of Marie Antoinette's hair. The other, a hair from the queen's father-in-law, Louis, Dauphin of France. The one containing a lock of the queen's hair is estimated to fetch between US$8,000 and US$10,000.
"The intrinsic value compared to the pearl is absolutely none, it's nominal," says Mr Correal.
"But there is such a personal side to this jewel. It's such an intimate jewel, holding a locket of the queen, and the fact that she wore them. It's fabulous."
The sale of royal jewels from the Bourbon-Parma family is set to take place in Geneva on November 14.
Marie Antoinette's jewellery collection is split across 10 lots, also including a set of pearl and diamond earrings, a diamond brooch, and a natural pearl and diamond necklace.
"It's been passed down through a family for 240 years. So, it's like a time capsule of French history," says Mr Correal.
"But you could arguably say the same from a painting, or from a piece of furniture, but you don't wear them. So, the most intimate, the most personal items of the queen are those that she had on herself."
APTN
