Hong Kong billionaire Joseph Lau won the Sotheby's auction for the "Blue Moon," a cushion shaped fancy vivid blue diamond, for US$48.4 million and has renamed the 12.03-carat stone the “Blue Moon of Josephine” in honor of his 7 year old daughter. It is the most expensive jewel ever sold at auction, and also the highest-ever price per carat of well over $4 million.

The previous record for the most expensive jewel bought at auction was for a 24.78-carat pink diamond dubbed the "Graff Pink." It sold for $45.6 million in 2010 to Laurence Graff, a London jewelry dealer.

Lau, a 64-year-old property tycoon, also paid $28.5 million for a 16.08-carat pink diamond earlier this week that he renamed the “Sweet Josephine,” also after his daughter. That adds to a growing collection for young Josephine. Lau bought a blue diamond in 2009 for $9.5 million, naming it the “Star of Josephine.”