A Hong Kong businessman just dropped a record-breaking $48.5 million on a rare, 12.03-carat blue diamond for his 7-year-old daughter.That price tag — the highest ever for a diamond or gem sold at auction — breaks down to a record-breaking $4 million-plus per carat, according to Sotheby's, the auction house behind the sale. To put that in perspective, each carat of this blue beauty is worth almost 1,000 times the average engagement ring in the U.S.The "Blue Moon diamond" was found at a mine in South Africa and has been graded the highest possible color quality for blue diamonds and deemed internally flawless by the Gemological Institute of America. It was up for grabs as part of Sotheby's major jewelry sale in Geneva this week.The diamond's name, fittingly, comes from the phrase "once in a blue moon.""This show-stopping blue diamond surely is a once-in-a-lifetime stone," David Bennett, Sotheby’s worldwide chairman of jewelry, said in a statement.Sotheby's only identified the buyer as a private collector from Hong Kong. But The Guardian and others have confirmed that it was purchased by billionaire Joseph Lau.Now named "The Blue Moon of Josephine," this giant rock isn't the first rare find Lau has gifted young Josephine. Just one day earlier, he reportedly dropped $28.5 million on a pink stone for her that he dubbed "Sweet Josephine."