Christie's said renowned jeweler Harry Winston was the buyer. The auction house had expected to fetch $30 million to $50 million for the nearly 19-carat, rectangular-cut stone, the largest fancy vivid pink diamond that it has ever put under the hammer.

It was the standout offering at Christie's fall jewelry auction in Geneva. The standing-room only ballroom broke into applause after the auctioneer struck down a hammer price of $44.5 million. That excludes the standard "buyer's premium" and other fees.

All told, the diamond went for $50.375 million, including the fees.

The stone once belonged to the Oppenheimer diamond family, and Christie's says it's among the most chemically pure gems — with little if any nitrogen.

Rahul Kadakia, Christie's head of international jewelry, said the auction house has sold only four diamonds weighing more than 10 carats of the same color in its 251 years in business.

Christie's chairman for Europe, Francois Curiel, called the stone the "Leonardo da Vinci" of diamonds.

"The 'Pink Legacy' ... brought this extremely high price of $50 million — so $2.6 million per carat, which is a world record price for a pink diamond. The previous record was $2.1 million, but for a much larger stone: Over 50 carats," Curiel said.

Christie's sale kicks off two days of jewelry auctions in Geneva. On Wednesday, Sotheby's will auction jewelry once owned by French Queen Marie Antoinette that hadn't been seen in public for 200 years.