See https://sothebys.gcs-web.com/static-files/5f0cd61b-8fde-4616-922e-d6c2341ae2ce
The brooch was sold for the then outstanding sum of 1,433,500 GBP
See http://www.sothebys.com/en/auctions/ecatalogue/2001/antique-and-20th-century-contemporary-jewels-l01751/lot.251.html
What is of significance is that the Sotheby's press release (first link) notes that the brooch to be auctioned had been in the Astor family until the early 1990s. For Sotheby's to make such an announcement suggests that there was documentation attesting to the provenance of the jewel -- as does the price it fetched at auction. I very much doubt if this jewel would have reached such a price based only on a supposition or claim that the bow brooch had belonged to the French Crown Jewels.
There seems to be considerable evidence that this is the brooch which Christie's advertised for auction in 2008, which was subsequently purchased privately by the Friends of the Louvre. Christie's original catalogue for 15 April 2008 https://www.christies.com/lotfinder/Lot/the-empress-eugenie-broochan-antique-diamond-bow-5059392-details.aspx A Christie's press release https://www.christies.com/presscenter/pdf/04222008/13443.pdf
The Friends of the Louvre is not a naive organisation. For it to purchase this jewel, it would have vetted the provenance with great care.
Because of this, I feel that the jewel was, when privately owned by a family, it was by members of the US Astor family, until, as the Sotheby's site notes, the 1990s.
To me the trail seems clear --- even though, I admit, I have not seen the papers proving this.
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