In March 1918 on a French battlefield somewhere east of Amiens, Australian troops encountered a young French boy kneeling over a family member killed by shellfire.

Heavy shelling from the retreating German artillery had laid waste to the nearby village and pulverised the landscape, and the boy had shrapnel wounds to his legs.

He gave his name as Jean Berthe and said he was an orphan.

The Australians gave him medical attention and when the Third Australian Pioneer battalion moved on, he went with them.

And so began a remarkable and enduring wartime mystery.

Initially, the boy was a camp follower running errands in exchange for food, but the troops soon became fond of him and made him an unofficial mascot.

They even had an Australian uniform tailored to suit his small frame.

With the Armistice on November 11, 1918, troops relished the prospect of returning to Australia.

One of them, a fisherman from Paynesville in eastern Victoria named Private Bob Simpson, also longed for home, but he couldn't countenance the thought of abandoning the orphaned boy to the chaos and further deprivation of war-torn France.

Author Sandra Hargreaves has spent the past few years piecing together Berthe's fragmented life.

Author Sandra Hargreaves has spent years researching Jean Berthe's mysterious life. ( ABC News: Tim Lee )

"I think [Simpson] was the one who instigated smuggling him back to Australia," she said.

It is possible that he was also smuggled aboard departing troopships from France to England and then on to Australia in a large blanket roll.

Another account mentions he was hidden from authorities behind a wall of soldiers' kit bags.

Berthe later stated that, dressed in his khaki uniform and presumably blending in with the disembarking troops, he simply marched down the gangplank unnoticed at Port Melbourne in June 1919.

Orphaned boy kept a town secret

Ms Hargreaves learnt of Berthe's story while researching the lives of local men who enlisted from the Paynesville area.

The story of the smuggled French orphan boy was familiar to older locals, but it was virtually unknown beyond the town.

For most of its history Paynesville was a quiet coastal fishing village, and Simpson and Berthe had good reason to keep their story under the radar of officialdom.

Jean Berthe (right) as a young man in his football uniform in Paynesville, Victoria. Date unknown. ( Supplied: Sandra Hargreaves )

At war's end, Army regulations expressly forbid troops bringing civilians, no matter their plight, into Australia.

Simpson never detailed how he got the orphan boy into Australia, however, there was talk humanitarian spirit won out.

"The story goes that he was smuggled on, and the commanding officer of the ship found him and turned a blind eye," Ms Hargreaves said.

Simpson, a commercial fisherman on the Gippsland Lakes, already had six children.

Berthe joined the family and took up fishing — he even played Australian rules football and won a trophy for best player.

In time, he lost any trace of a French accent and forgot his mother tongue.

He married a local woman in 1943 and the couple ventured up and down the east coast chasing fish.

Berthe is remembered as a man of exceedingly few words, and never mentioned who his parents were or the circumstances of his discovery by the Australians in 1918.

He barely spoke of his childhood in wartime France and only ever remarked that he had left a battlefield and had no wish to ever return.

"He was a very private man and it was kind of like putting a jigsaw together, finding a piece here and a piece there, and gradually it began to crystallize," Ms Hargreaves said.

But like Berthe's few professed particulars, the official records were fragmented.

Janet and Jean Berthe walk together, circa early 1950s. ( Supplied: Sandra Hargreaves )

He stated he had been born in Amiens in 1906, but Ms Hargreaves scanned the census records of hundreds of towns across France and found nothing that matched.

"Maybe his name wasn't Jean Berthe," she said.

"Perhaps he'd been born illegitimately and had a different name, perhaps he hadn't been born in Amiens at all."

And perhaps Jean Berthe was so traumatised by the horrors of war that he simply couldn't remember much.

We will never know.

A father figure to those in need

Berthe's illegal entry to Australia in 1919 left him in limbo as a non-citizen.

Despite concerted efforts over several decades to be naturalized, his attempts seemed to have stalled in federal bureaucracy.

He tried to enlist in World War II, but was rejected when his French origins were discovered.

The Army medical did however give credence to the story of him being wounded as a boy, when the doctor found extensive scarring on his ankles consistent with shrapnel wounds.

Jean and Janet Berthe had no children, but Jean was very community-minded, growing vegetables and distributing fish to needy families.

To Leigh Robinson, now 88, he was like a father figure.

"Dad got killed in 1941," Mr Robinson said.

"I was 11. There was no widow's pension in those days.

"[Berthe] was just a loving, caring, quiet man. I've never known a man as quiet in my life."

To Leigh Robinson, 88, Jean Berthe was a father figure in their small community of Paynesville. ( ABC News: Tim Lee )

Berthe died in 1974, seemingly taking many secrets to his grave.

His wife survived him by a decade, but if she knew more of her husband's childhood story, she never revealed it to anyone.

Locals knew of Berthe as 'Jeannie the Frenchman'.

Ms Hargreaves has written and published a book, 'Jean Berthe — The Quiet Frenchman' to mark the Centenary of the Armistice.

The book details how at least two other orphans were brought back to Australia from the Western Front by Australian troops at the end of World War I.

The war left an estimated 900,000 orphans in France alone.

Ms Hargreaves believes there must be other traces of this mysterious man that have yet to come to light.

She has vowed to keep searching.

"Maybe someone will uncover something one day," she said.

Watch this story on Landline on Sunday at 12:30pm.