But now, an amateur historian has exposed the compelling tale of adventure, incest and skullduggery as an elaborate fiction, even if the true story remains a mystery for now.
More than a century on, the bones, encased in a glass-faced coffin, have been packed off to a forensic lab outside Paris in the search for clues.
When masons digging a cellar at the manor found the skeleton in 1913, neither police nor the local parish priest took much interest, and no investigation was ever held.
It was 20 years later, in 1933, when a local newspaper, Le Courrier du Centre, unspooled a series of articles purporting to tell Ernest's story.
The newspaper claimed that the bones belonged to the manor's former master, Ernest de Fontaubert, who had taken off with his sister Ernestine in 1850 to join the California Gold Rush.
On his return to France, the story goes, his little brother Arthur killed him with a hatchet, furious over a supposed incestuous relationship between Ernest and Ernestine.
The story unfolded in florid detail, claiming that the incestuous couple had buried still-born children at the manor.
The newspaper held that when Arthur killed Ernest, he also butchered two bullocks at the entrance of the manor, hoping that the smell of the rotting animals would hide that of his brother decomposing under the floorboards of his own bedroom.
The gripping tale, told with a high literary standard, entered into the annals of the region, becoming more accepted as fact with each generation.
By 1958, the story even inspired a novel, "La Terre Aux Loups" (Wolf Country) by Robert Margerit, a prolific author and journalist.
When amateur historian Bernard Aumasson came along in 2011, he took one look at the story and decided it was "as plain as day" that it was just that -- a story.
Working with an American genealogist, he determined that Ernest de Fontaubert had indeed left for the United States -- but was never to return.
According to a search of the archives in Calaveras, the California county where Ernest and Ernestine reportedly lived during the Gold Rush, Ernest was murdered near Cave City, robbed of the gold he had on him and left for dead in February 1862.
Encouraged by this evidence, Aumasson began poking holes into the received wisdom, and has inspired several history buffs to join his quest for the truth.
"After all, there was a corpse, and it was in a strange place for a dead man," said local police colonel Patrick Chabrol, who took it on himself to drive the remains to the forensic lab in his own vehicle.
The experts at Cergy-Pontoise outside Paris will analyse the bones to establish their age and sex and possibly determine the cause of death.
Gilbert Chabaud, who has owned the Montcigoux manor since 1977 and is the mayor of the hamlet of some 400 inhabitants, said he was sad to say goodbye to "Ernest".
But Chabrol reassured the townsfolk: "As soon as he has had these little tests, he will return to his place. We will return him to the village."