During a dive around the wreck of HMS Opal, off the Orkney Islands, two months ago, amateur diver Peter Brady, 51, spotted the engraved engagement ring from his sweetheart Florence. The inscription in the ring helped in identification. It says: "To Stanley from Flo, March 1916."
Mr Cubiss, 25, who worked in the ship's engine room, perished with 187 other men when the Opal, along with HMS Narborough, ran aground in a snowstorm on January 12, 1918.
Mr Brady and diving partner, Bob Hamilton, 61, found the ship's casualty list on the internet and managed to track down Stanley's 78-year-old nephew, Malcolm Cubiss.
"I received a call out of the blue telling me that divers had found this ring," said the retired brigadier from York.
"My uncle is often spoken of in the family and I know the tragedy of the Opal well. They came to show me the ring and I was astonished. It's a million-to-one chance." Link