An exceptionally-sized diamond ring bought for £10 (HK$100) at a junk sale was sold at a staggering £656,750 at Sotheby’s in London yesterday – after it turned out to be a 26.27ct cushion-shaped white diamond.

According to 77 Diamonds website, the diamond was snapped up at a junk sale in west London for £10. The buyer thought it was a piece of costume jewellery.

However, it has been confirmed by the Gemological Institute of America that the diamond is actually a genuine one from the 19th century.

Tobias Kormind, managing director of Europe’s largest online jeweller 77 Diamonds.com, says the large diamond had been “dramatically undervalued all these years”.

Junk sale diamond ring bought for £10 worth a fortune

He adds, “If ever there was a great return from investing in diamonds, this is it.”

It is believed that the ring was once owned by the royal family or a person of great wealth. “It originated from the 1800s – before the discovery of modern diamond mines and a time when very few diamonds were available,” Kormind says.

“The new owner is likely to re-cut it into a modern diamond that will emit even more sparkle and potentially be worth a multiple of today’s price.”