A mother-daughter duo sauntering through London's Crystal Palace Park during an outdoor taping of BBC's Antiques Roadshow were shocked to learn that a diamond ring they found stashed in "mum's" sock drawer was a 4-carat, platinum-set treasure worth £20,000 ($25,800).

The mom and daughter hadn't intended to get the ring appraised that day, but there was no queue to meet with fine jewelry consultant Joanne Hardy so they decided to give it a go.

The mom explained to Hardy that she and her daughter had been helping out her "mum" clear out some old items when they happened upon the ring that had been balled up in a sock and hidden in a sock drawer.

“No! I don’t believe that," Hardy exclaimed. "And it could have gone in the washing machine."

The guest added, "We could have just bundled everything up.”

“Given it to the charity maybe," Hardy said. "Oh my goodness!”

“When I said, ‘Mum, is this your ring?’ she said, ‘Oh yes I kept it in there so I didn’t lose it.’”

The mom said she was pretty sure it was given to her mum by her late grandfather.

After inspecting the ring, Hardy reported to the guests that the ring dates back to about 1915 and was crafted in platinum.

“It is absolutely superb," she said, adding that the diamond predates the modern brilliant cut.

"It is what we call a transitional cut," she said. "It’s [has] a soft, really soft look about it. You’ve got the facets, but nothing's sharp. The modern brilliant cut, to me, is quite brash, but this has such an air of sophistication."

Hardy said the diamond weighed nearly 4 carats and displayed fine clarity, except for a tiny natural flaw on the side. She showed the guests that one of the prongs was damaged and needed to be re-tipped.

“There’s one claw there that has come adrift,” Hardy joked.

Then the mother-daughter duo learned that if they were to sell the ring at auction, it would fetch about £20,000.

“Wow. Oh gosh. Oooh," the mom said.

“I won’t be taking it off my finger,” added the daughter.

Then the mom realized that they had work to do: “We'd better get that claw fixed quickly. Wow. Wow.”

“It is such a stunning, stunning ring," Hardy added. "It’s absolutely lovely."

Credits: Antiques Roadshow screen captures via BBC.co.uk.