The owner of the ring had not realised it was in fact a 19th century diamond until earlier this year when she was encouraged by a jeweller to have it valued.
Bought at a car boot sale at West Middlesex Hospital in west London, the claw-set 26.27ct cushion-shaped diamond ring was taken to Sotheby’s to be valued earlier this year.
A note in Sotheby’s catalogue said: “It was only in the past few months that the owner decided to see if the ring had any value and asked Sotheby’s to appraise it. Much to the owner’s surprise, the ring turned out to be genuine.”
Head of Sotheby’s London jewellery department Jessica Wyndham said the owner had not realised it was a real diamond as its sparkle was not noticeable. This is because it is an old style cut diamond, where the light does not reflect as it would from a modern stone cutting where the ‘sparkle’ is more intense.
The diamond has a colour grade of I and impressive clarity grade of VVS2.
It will be offered as part of Sotheby London's Fine Jewels sale on June 7.