A woman from Northumberland has discovered that her collection of cheap "costume jewellery" included a diamond worth an estimated £2 million.
The woman, who is in her 70s and does not want her identity revealed, submitted her collection to Featonby's Auctioneers in North Shields for auction.
Mark and Casey Lane, Featonby's Auctioneers.
When storing the collection at their office, one of the Featonby's team made the "passing" suggestion that someone test the stone - which they fully expected to be an imitation.
To their "disbelief", the pound-coin-sized piece turned out to be genuine.
"When holding the stone beside our diamond tester, it came back as a genuine diamond leaving all involved in disbelief," said Casey Lane, Managing Director at Featonby's.
"The stone was then sent to our partners in Hatton Garden, Swan & Co, who specialise in bespoke jewellery and gemstones.
The piece, which the auctioneers have tagged 'Secret Stone' due to its discovery story, will be up for auction on the 30th November at 12 noon live from Featonby's.