LONDON -- Sotheby's is displaying the startling "pink star" diamond in London before it's being auctioned in Hong Kong next month.

The company says the gem should fetch more than $60 million when put on the block on April 4, which would represent a record for a pink diamond sold at auction.

It said Monday that the 59.60-carat gem is the largest flawless fancy pink diamond ever graded by the Gemological Institute of America.

Sotheby's jewelry division chief David Bennett said the gem's size and colour "surpassed any known pink diamond recorded in history." It was mined in Africa in 1999.

The company sold the "Blue Moon of Josephine" diamond for $48.5 million in Geneva in 2015.