The "Blue Moon" diamond sold for an astonishing $48.5 million this week at Sotheby's in Geneva.

The stone, just over 12 carats, was expected to fetch between $35 million and $50 million. It's the highest price ever paid for a blue diamond, so named because of the expression "once in a blue moon" in a nod to how rare it is.

Hong Kong businessman Joseph Lau, who's worth roughly $10 billion, who was the lucky winner of the jewel, which he renamed "The Blue Moon of Josephine," in honor of his seven-year-old daughter.

Auctioneer David Bennett said it was a historic purchase:

Tonight we set a new world record, a new auction record for any diamond, any jewel, any gemstone, with the sale of the Blue Moon diamond."

The blue diamond wrapped up a flurry of shopping for Lau, who dropped $28.5 million the night before on a pink diamond that he promptly named "Sweet Josephine" (this girl really ought not to expect much for Christmas).

Lau, incidentally, was sentenced to more than five years in prison last year in Macau for bribery and money laundering, but has avoided serving time because he didn't attend the trial and has avoided returning to the territory.

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