In 1937 Sotheby's held an auction in London which drew massive interest, to the extent that the BBC installed a microphone to make a live broadcast at the end of the sale. Two items of significance were to be auctioned: the Cowdray black pearls and a diamond necklace which had formerly belonged to Marie Antoinette.
[The microphone can be seen in this photo held by Topfoto
http://www.topfoto.co.uk/imageflows2/?s=EU054450 ]
The Cowdray pearls failed to sell but the diamond necklace was sold to the Maharajah of Darbhanga for 15 thousand pounds.
[Topfoto photo of the Maharajah leaving the sale
http://www.topfoto.co.uk/imageflows2/?s=EU054381 ]
The necklace,
http://www.topfoto.co.uk/imageflows2/?s=EU049988 which came with sworn affidavits attesting to its origin and subsequent provenance, was sold by the then joint owners, the Archduchess Blanca of Austria and her sister, Princess Beatrix of Massimo.
The Maharajahs of Darbhanga had a long history of acquiring jewels of historic significance, which they wore on numerous occasions. I suspect, however, that this necklace may have been worn by the wives of the Maharajahs, although that may just be fanciful thinking on my part.
These two sites give some interesting information about the Darbhanga collection, which the first one says was even finer than the collection of the Nizams of Hyderabad.
https://www.livehistoryindia.com/forgotten-treasures/2017/07/13/lost-jewels-of-darbhanga https://www.indiatoday.in/magazine/special-report/story/19820815-darbhanga-provides-a-classic-study-of-the-decline-and-fall-of-indias-feudal-ruling-class-772064-2013-10-04 The necklace remained in the Darbhanga collection until it (along with other jewels) was sold in 1967. Some sites say the Marie Antoinette necklace was sold to Nanubhai Jhaveri, a jeweller in Bombay.
What happened to the necklace then is a bit of a mystery, although it surfaced at a Christie's auction in London in July 1971 but remained unsold as the top bid of 120 thousand guineas was below the reserve price.
There doesn't appear to be any public record of what happened subsequently, or where the necklace is today.