A rare antique diamond necklace which was worn at two British coronations is expected to sell for more than £1 million when it goes under the hammer.

The 18th century diamond piece of approximately 300 carats was worn to King George VI and Queen Elizabeth II’s coronations by members of the Marquess of Anglesey family, who had it in their collection for around 100 years before it was sold to a private collection in the 1960s.

It may also be linked to Marie Antoinette as some jewellery historians believe it features diamonds from the infamous necklace which created a scandal for the Queen of France.

What became known as the “Affair of the Necklace” was an incident that occurred when Marie Antoinette was falsely accused of not paying for an extravagant necklace, which was actually taken by a trickster who claimed to be acting on her behalf.

The exact origin story of the necklace going for auction is not recorded but it is thought to have been created in the decade before the French Revolution, likely for royalty or a high-ranking aristocrat.

After not being seen publicly for 50 years, the unique necklace is estimated to sell for 1,800,000-2,800,000 dollars (£1,348,416 to £2,097,536) when it is offered in the Sotheby’s Geneva sale in November.

The piece is composed of 500 diamonds which feature on three ropes which gather to create naturalistic-looking diamond tassels.

Andres White Correal, the chairman and head of the royal and noble sales at Sotheby’s for Europe and the Middle East, told the PA news agency: “I think that the most important part, other than the value of the diamonds, is the fact that it has survived.

“You only see these things in museums when it has been from royal families who are still reigning, like the collections here in Britain, or when you go to former imperial and royal collections in places like St Petersburg or Moscow, where you can see the collections of the Tsar…

“So yes, you go to a museum and you can see a jewel of this level. Normally, you don’t see it in private hands.”

Mr Correal said he hopes the necklace is acquired by an institution or for a private collection which “appreciates” the jewels.

He added: “I would either would love an institution to have it so that most people could enjoy it, go look at it and learn about jewellery from the 18th century and how this near miracle of still being together, rather than having been separated, (and) how people wore jewellery in the 18th century.

“And if that wouldn’t be the case, I would love for the necklace to go to a solid and wonderful collection where a person who appreciates this type of jewel would safe-keep it for the next generation.

“I don’t think that objects like this you actually own, you are merely the custodian of such an incredible object to pass it on, either to a new generation or to an institution where many other people can enjoy it.”

The necklace will embark on a global exhibition tour with a stop at Sotheby’s London auction house until Wednesday before it travels to Hong Kong, New York, Singapore, Taipei and Dubai.

It will be auctioned at Sotheby’s Royal and Noble sale on November 11 at the Mandarin Oriental in Geneva.