The Unique Pink, a 15.38 carat fancy vivid pink diamond, is to auction on May 17.
 The Pink Unique is valued at up to $38m |
The lot is valued at $28m-38m ahead of Sotheby's Magnificent Jewels and Noble Jewels sale in Geneva.
David Bennett, worldwide chairman of Sotheby's jewellery division, comments: "It is difficult to imagine a diamond that better illustrates the term Vivid Pink than this outstanding stone.
"The colour is simply astonishing and, for its size, it is in my experience truly unique."
Several diamond sales are coming up over the next few weeks, with Christie's offering potential record breaker the Oppenheimer Blue.
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