The royal jewels are expected to go for more than $700,000. The necklace is made of rubies, diamonds and 21 natural gray pearls that date to the 1780s. The pearls are suspended from a diamond collet along a ruby collar.

The Queen of France was executed for treason during the French Revolution in 1793. The pearls passed to Lady Elizabeth Sutherland, Duchess of Sutherland, and the necklace was made in 1849, according to Christie's Web site.

Pearls that Marie Antoinette purportedly gave to a British countess for safekeeping after the French queen was imprisoned will go up for auction, Christie's said Thursday.

The pearls, now part of a necklace that also contains rubies and diamonds, are expected to fetch up to $800,000 when they are sold in December.

The pearls were reportedly given to Elizabeth Leveson-Gower, wife of the British ambassador to France during the French Revolution, and were intended to help the queen if she managed to flee the country, said Raymond Sancroft-Baker, senior director of Christie's Jewellery in London.

"She thought, as one would, that she was going to get out of it," he said. Instead, Marie Antoinette died by the guillotine in 1793.

There is nothing in writing to verify the pearls owned by the Countess of Sutherland had belonged to the French queen, but circumstantial evidence indicates the story is true, Sancroft-Baker said.

"They were friends, they had children of the same age, and Lady Sutherland supplied various things to her when she was imprisoned," Sancroft-Baker said. "Logically she couldn't give them to just anybody. A foreign diplomat with diplomatic immunity was the one person who wouldn't be searched."

Lady Sutherland is also believed to have aided the Austrian-born queen, her husband King Louis XVI, and their family in a failed attempt to flee France in 1791.