The stunning 9.75 carat, pear-shaped diamond was bought by a Hong Kong private collector after 20 minutes of competitive bidding yesterday, Sotheby's said.
The price also set a new world auction record for price-per-carat for any diamond, the auctioneers said.
The jewel had been owned by Rachel Lambert otherwise known as Bunny Mellon, the art collector wife of the late philanthropist and racehorse breeder Paul Mellon. She died in March aged 103.
"Mrs. Mellon's diamond absolutely deserves the place in the record books that it achieved," said Gary Schuler, head of Sotheby's jewelry department in New York.
It was the highlight of a collection of Mellon's jewels and objects of vertu that Sotheby's sold for more than USD 42 million in New York yesterday, well above the pre-sale estimate of USD 19.2 million.