Sotheby's auction house said Thursday it will auction off an extremely rare and historically important pink diamond, believed to have once belonged to Napoleon's niece. The fancy vivid pink diamond, weighing 8.72 carats, is "extremely rare", the auction house said, pointing to its classic non-modified cushion cut, which is highly sought after but unusual in pink diamonds.

The stone, which is mounted on a ring and sparkles with "clarity and mesmerising colour", is believed to have been part of the collection of Princess Mathilde, niece of French Emperor Napoleon I, according to the Gemological Institute of America (GIA). Sotheby's hopes to rake in US$19 to 24 million for the rock.