Geneva—A record-breaking fancy vivid blue diamond once belonging to American horticulturalist, philanthropist, and art collector Rachel “Bunny” Lambert Mellon is returning to the auction block.

“The Mellon Blue,” a 9.51-carat pear-shaped diamond with internally flawless clarity, is estimated to achieve $20 million to $30 million at Christie’s Geneva in November. 

The diamond, which was recently set as a ring, is a “rare expression of nature’s brilliance,” said Christie’s, remarkable for both its intense color and its extraordinary purity. 

The piece will lead the Magnificent Jewels live sale, set to take place Nov. 11 at the Four Seasons Hotel des Bergues in Geneva.

Mellon, who held the blue diamond in her possession for decades, was the second wife of wealthy horse breeder Paul Mellon. 

In the 1960s, she redesigned the White House Rose Garden at the request of President John F. Kennedy, adding more open space and introducing American species of plants to the garden. She was also involved with design projects in France that included the home of Hubert de Givenchy and the gardens at the Chateau de Versailles.

Her refined taste extended from her interiors and gardens to her jewelry, Christie’s said. 

She died in 2014 at the age of 103, and later that same year, the diamond was offered at a Sotheby’s sale of her property. It set two records when it sold for $32.6 million—price paid for a blue diamond and price per-carat for any diamond. 

The diamond has not been seen publicly since that auction. 

“This stunning fancy vivid blue diamond, once belonging to America’s Garden Queen, and is among the finest colored diamonds to appear for sale at auction,” said Christie’s International Head of Jewellery Rahul Kadakia. 

Kadakia also noted that Christie’s has sold nine of the top 10 jewels at auction in the first half of the year. 

Prior to the Magnificent Jewels sale, The Mellon Blue will be displayed at Christie’s Hong Kong from Oct. 23-28 and from Nov. 7-11 at the auction venue in Geneva.