He stands in full Scottish military dress, a proud member of the First Cameron Highlanders with a castle behind him and his future ahead of him.

This extraordinary 100-year-old photograph was colour-tinted in the Edwardian fashion of the day. To our modern eyes, it looks like it could illustrate a tourist-friendly tin of Scottish shortbread.

But this is not some young, ruddy-cheeked clansman in the kilt and the sporran, but a lad from the Mendips whose Somerset burr sparked a century of tragic mystery – a conundrum that has finally been solved by a West author.

Arthur Blakeman's name is still carved on the memorial to the Great War in the centre of Weston-super-Mare. A son of Cheddar, he joined the Army straight from school in his mid-teens, in 1910.

But Arthur Blakeman's service and death in the first battle of Ypres, in the early days of the horrors of the trenches of the First World War, has no official record. His name does not appear on the Menin Gate, and his existence is not registered by the Commonwealth War Graves Commission, whose on-line database has provided hugely valuable information for historians.

What happened to Arthur, the soldier who apparently vanished without a trace, always mystified his family. So when his niece, Jeannette Climmer, from South Gloucestershire, enlisted the help of Wiltshire-based author Richard Broadhead, it was a challenge that they thought he wouldn't be able to meet.

"Jeannette said that the family had tried for years to find out what happened to Arthur," said Mr Broadhead, whose research into the fallen soldiers of the Great War has sparked several local history books.

"She said, 'You'll never be able to find out what happened to him', so that was a bit of a challenge. It took years of investigation, but now the case has been cracked, as it were," he explained.

Arthur's grieving family would have been given the standard cursory letter of condolence, saying he was missing or killed in Flanders in November 1914. Generations and decades later, the family's efforts to find out more hit a dead end – no record of their long-lost uncle could be found.

"In the end, the truth was ridiculously simple but it explained why they couldn't find him," said Mr Broadhead. "On the Menin Gate, and with the War Graves Commission, he's down as 'Arthur Blackmac', not 'Blakeman', so it was no wonder no one could find anything out," he added.

"I've written to the Commonwealth War Graves Commission and they asked for evidence. I've presented all the evidence there is. His Army records show that 'Arthur Blackmac' was born in Cheddar, and I've shown that there aren't any birth records for a birth in Cheddar in 1895 by that name.

"I've shown that when he joined the Army he was Arthur Blakeman, but somewhere in the Scottish regiment he was assigned to, someone wrote his name down as Blackmac and it stuck on his records. Maybe the Scottish officers couldn't understand his Somerset accent, or maybe it was just written down with poor handwriting and copied wrong.

"I've had meetings with the CWGC showing them all this, but it's still not enough. I've been working on it for five or six years and it's wonderful to be able to show the family what actually happened to him, but to get closure we need to have his name changed," he added.

A spokesman for the Commonwealth War Graves Commission said they would investigate the issue. "We have investigated this application, but unfortunately the only thing that supports the name being changed is the birth certificate provided," said a spokesman.

"Other documentation from official sources support the name as we have it, but the case is not closed and we are always open to hearing more information," he added.