Mined from South Africa's Cullinan mine — the same source as several British Crown Jewels — the cushion-shaped stone carries the highest possible color and clarity grades a blue diamond can receive.
It went to auction at Sotheby's Geneva in 2015 as one of the largest internally flawless blue diamonds ever offered.
Hong Kong tycoon Joseph Lau paid $48.4 million, had it set into a ring, and renamed it after his daughter Josephine.
He did this exactly one day after paying $28.3 million for a separate pink diamond at the same auction house — also for her. Two diamonds, one week, one seven-year-old.
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