Sergeant Charles Reid, a soldier from Newfoundland, was killed on July 1, 1916 - the first day of the Battle of the Somme.
Sgt Reid’s personal effects included a rose-gold locket made in Oban, Argyll, which included a portrait of him and of a unknown woman.
The soldier’s relatives suspect the woman was from Scotland and are appealing for information in the hope that they can identify her before the centenary of Sgt Reid’s death.
Sgt Reid served with the Royal Newfoundland Regiment which was part of the British Army as Newfoundland was not then part of Canada.
He was killed at Beaumont-Hamel, one of the most disastrous battles of what was to become the costliest day in the history of the British Army.
Of the 780 men who attacked the German trenches on the day only 68 survived unscathed - with Sgt Reid among those killed and laid to rest in a war grave in France.
But when his personal effects were returned to his family, they were perplexed to find a rose-gold locket, with an image of a uniformed Reid and a mystery lady inside.
Now - nearly a century later - Ralph Reid, the great-grand nephew of Sgt Reid has contacted a jeweller - who has discovered that the lady was likely from Oban, Argyll and Bute, where the locket was made.
The jeweller was able to able to track down the piece to J McGilvray and Son on George St, in Oban, after noting that the locket was being kept in its original box, which contains the
Pat Thompson - owner of Diamond Design in St John’s, the capital of Newfoundland and Labrador - provided the expert insight.
He said: “It immediately struck me and being a big fan of history, I started to quiz Ralph a little bit about the locket.
“It became apparent to me that there was a great deal of mystery attached to this.
“She was probably in Oban or up in that area and never knew what happened to her Charlie. A very sad story, but very wonderful.”
Ralph Reid said: “We don’t know who she may be.”
“I was looking at it and was wondering what kind of gold it was, if anybody had any knowledge of where it came from or what value it would be.”
Mr Thompson and Mr Reid have contacted the still-open jewellers in Oban, who have said that their records do not date back to 1916.
Now the hunt is on for anyone in Scotland who may recognise “the Lady in the Locket” - and put to rest the mystery of Sgt Reid’s secret sweetheart.
Sgt Reid was killed at just 30 years-old - but in the ultimate family tragedy his younger brother Alfred was also wounded at the same battle and died seven weeks later in London.
As WWI began Newfoundland was still under British rule, and the island - off Canada’s east coast - was quick to raise a regiment of around 1,000 men.
The Royal Newfoundland Regiment fought in Gallipoli, before moving to the Western front in March 1916.
They were among the third wave of attackers on the first day of the Somme - after the two waves in front of them were wiped out.
Reid and his fellow-soldiers left the trenches at 9.15am - immediately coming under heavy fire from German troops, dug in just 300 metres away.
When the attack was called off 90% of the regiment had been wiped out.
A monument now stands at Beaumont-Hamel to honour the 200 members of the regiment who lost their lives there.
50 or more of the soldiers are unidentified - and Sgt Reid’s headstone notes that his body lies among them.