A rare, pear-shaped, vivid pink diamond will go under the hammer at auction in Geneva next month, where auctioneers expect the unusual gem to fetch £27 million.
The 'Unique Pink', described by Sotheby's as 'supremely rare and exceptional', weighs 15.38 carats.
David Bennett, worldwide chairman of Sotheby's international jewellery division, told Reuters: "The Gemological Institute of America, the highest body for grading diamonds, have given this stone their highest possible grading, which is vivid pink".
"It's the largest pear-shaped fancy vivid pink diamond ever to be offered at auction."
The discovery of gem-quality pink diamonds is rare, according to Sotheby's, which will auction this one as part of its "Magnificent Jewels and Noble Jewels" sale in Geneva on May 17.
"We're estimating between $28-38 million," Bennett said of pre-sale estimates during a preview of the diamond in London.
"There have been a couple ... of stones that have sold for around £1.4 million per carat or a little more historically so it seems to be perfectly correctly estimated... We will see."
Earlier this week, a 10.10 carat oval, internally flawless, fancy vivid blue diamond sold for £22.5 million at an auction held by Sotheby's in Hong Kong.
Other items to go up for sale in the same auction include 'The Emperor Ruby' a ruby and diamond ring estimated to sell for between £3.6 million and £5.75 million and a diamond brooch expected to sell for between £7.2 and £10.01 million.
The most expensive watch ever sold at auction fetched just under $24 million in November 2014. The gold pocket watch was made by Patek Philippe, and is the most complex ever made without the use of computer technology.
The Henry Graves Supercomplication was commissioned in 1925, and took eight years to make.
The world's most expensive stamp sold at auction in 2014 for over $9 million.
The British Guiana One-Cent Magenta is as rare as a stamp can get. British Guiana was one of the first countries in the New World to start issuing stamps, but in 1856, they ran out, and asked the local newspaper printer to produce extras.
There were two denominations: the four-cent, which is very rare, and the one-cent - of which only one has ever been discovered.
In May 2015, an anonymous London businesswoman snapped up the licence plate KR15 HNA for £233,000, making it the most expensive standard number plate ever to be sold in the UK.
Queen Victoria's bloomers sold at auction for £6,200, along with a pair of her silk stockings.
They have a 52-inch waist, and belonged to the monarch in the 1890s - "towards the end of her life when she had eaten a lot more than most people could afford to," said auctioneer Michael Hogben. In today's sizing, they'd be a size 26.
In 2014, a three-year-old slice of cake sold at auction for $7,500 (£4,800). The reason the stale cake was in such demand was that it was from the marriage of Prince William to Kate Middleton in 2011.
The buyer said he intended to give it away as part of promoting his Silicon Valley start-up.
A British coin sold at auction for a record-breaking £430,000 in 2014. After fees, the buyer paid £516,000 - making it the most expensive modern British coin ever to be sold.
The coin is only one of two in existence. It was a 'proof' for a gold sovereign which was meant to be produced to commemorate the coronation of Edward VIII in 1937. However, Edward abdicated in 1936, so the coronation never happened and the coins were never made