Cash is still king, for now.

A 101.38-carat diamond was sold by Sotheby's for HK$95.1 million ($12.3 million) to an unknown buyer using traditional currency, disappointing cryptocurrency fans who had hoped the offering by Sotheby's would mark another milestone in mainstream acceptance of digital assets.

Prior to Friday's sale, the international auction house said it would take Bitcoin or Ether as payment for the pear-shaped flawless diamond, which fetched less than the estimate of as much as $15 million in the single-lot offering in Hong Kong. The auction was livestreamed and attracted no more than a dozen bids.

Earlier in the week, Sotheby's said it was the most expensive physical object ever publicly offered for purchase with cryptocurrency

Auction houses are increasingly accepting cryptocurrencies for payment, with Phillips offering a piece from street artist Banksy last month for Ether or Bitcoin. Christie's accepted payment in Ether in March for the record $69.3 million sale of Beeple's “Everydays: the First 5,000 Days.”