The Vignacourt Youth Assembly and documentary-makers David Chour and Emmanuel Louisy-Gabriel are investigating the life of former Horsham mayor Robert Edward Charles.

His picture was among thousands of photographic glass slides discovered in the attic of a derelict house in Vignacourt, France, after almost a century.

Sergeant Charles was briefly in the small village, near the Western Front, while serving in the First World War.

His service in the 29th Australian Infantry Battalion earned him a Meritorious Service Medal.

Wimmera woman Sally Bertram said she recognised her grandfather the moment she saw the portrait.

She had taken interest in the Lost Diggers of Vignacourt photo collection because of where they were taken.

"I just happened to know from his diary and battalion book he had been in Vignacourt," she said.

"So I went looking and found his photo."

The family's discovery was just the beginning of the story.

Mrs Bertram and her mother, Virginia Easson, who was Sgt Charles' youngest daughter, have been searching for more information ever since.

Friends and researchers from France and Australia have helped them shed light on the story, including a family Sgt Charles stayed with in Calais during his time in France.

Mrs Bertram said she was excited for the delegation to arrive on Saturday.

The documentary-makers already have interview footage of her mother but are keen for more.

Mrs Bertram said the youth assembly wanted to learn as much about Sgt Charles' legacy as possible.

In addition to being a former mayor, Sgt Charles was a life governor of Horsham's hospital, a staunch supporter of Horsham's racing, trotting and football clubs, and heavily involved in the RSL, which was historically the Returned Sailors and Soldiers Imperial League of Australia.

Sgt Charles was also instrumental in involving young indigenous men in football.

Horsham RSL and Horsham Rural City Council will host the delegation on Sunday.

RSL senior vice-president David Eltringham said the day would start at Horsham Civic Centre, where Sgt Charles is mentioned on the past mayors honour board.

"We will then take them to the RSL and show them various memorabilia and records we have of Sgt Charles," he said.

The delegation will eat a traditional Sunday roast lunch, before a series of speeches.

In the afternoon, the delegates will help plant a lone pine at Horsham cenotaph.

"There were originally eight, which represented the eight months the Anzacs were at Gallipoli," Mr Eltringham said.

A tree died and will subsequently be replaced.

Mr Eltringham said the delegation's visit was especially significant, given this year's First World War centenary commemorations.

"We look forward to the French people going back with vivid and happy memories of Horsham," he said.