The Wittelsbach-Graff Diamond is to appear before the public for the first time in more than half a century.
The 31.06 carats rare, greyish-blue gem will display at the Smithsonian's National Museum of Natural History, from January 28 to August 1 next year.
Billionaire Laurence Graff has
repolished the stone, making
it 'eternally flawless'
Billionaire Laurence Graff purchased the diamond at auction in December 2008. He then re-polished the stone and brought more life and colour to it.
Graff's work on the diamond has made it eternally flawless, according to the Smithsonian.
It will be exhibited in the Smithsonian's National Gem Collection in Washington, which also has the Hope Diamond on permanent display.
Many believe that the Wittelsbach-Graff jewel was discovered in the same Indian diamond mine as the Hope Diamond - to which its colour and size has been compared - and the Evening Star Diamond, which sold for $5.4m in New York, earlier this month.
Its provenance can be traced back as far as 1662, when Philip IV of Spain gave the stone to his daughter as gift for her engagement to Emperor Leopold I of Austria.
Smithsonian scientists will reportedly investigate the diamond's origins during its time at the museum.
In October of this year, another unique and legendary jewel, the Annenberg Diamond, sold for $7.7m at Christie's.
Once owned by Leonore 'Lee' Annenberg, the world's 403rd richest person (according to Forbes), it was sold following a tour to find a suitable buyer which included Geneva, London, Hong Kong and Los Angeles.
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