A 7 year old little girl is now the very lucky owner of the most expensive diamond ever sold at auction. Her Hong Kong businessman father reportedly bought the gem for a record $48.5 million. Yes, for a 7 year old. The rare diamond is a 12.03-carat blue diamond – broken down to $4 million per carat. The “Blue Moon Diamond”, now named “The Blue Moon of Josephine”, after the child was found at .