After the French Revolution, eight-year-old Louis XVII was taken to prison and never seen in public again.

Louis XVII (1785-1795), Dauphin of France. Christophel Fine Art/UIG/Getty Images

Louis-Charles de France grew up in the gold-trimmed rooms of Versailles, the happy, handsome and charming son of Louis XVI and Marie Antoinette. At the age of four, he became the heir to the French throne when his brother died, and from that day forward, the whole palace staff bowed to his every desire.

But the French Revolution destroyed his family, and the once carefree child—an orphan by the age of eight after his parents’ execution in 1793—was horribly abused and neglected, isolated in a prison cell in the Paris Temple. Vilified as the “wolf cub,” the “son of a tyrant” and the “bastard,” by 1795 the newly styled Louis-Charles Capet was unrecognizable, covered in sores and his belly distended from malnourishment.

Finally, his jailers called in Philippe-Jean Pellatan, a respected doctor who was horrified by the condition of the young Dauphin, or heir apparent, writes Deborah Cadbury in The Lost King of France. “Unfortunately, all assistance was too late,” the doctor recalled of the boy who was once destined to become King Louis XVII. “No hope was to be entertained.”

On June 8, 1795, Louis-Charles died of tuberculosis in the arms of one of his jailers. He was only ten years old.

An illustration of Louis XVII of France, who died in the Temple prison being taken up into heaven. Adoc-Photos/Corbis/Getty Images

The revolutionary government quickly sprang into action. The child’s body, so neglected in life, was hovered over in death. Dr. Pellatan performed a detailed autopsy, and found physical evidence of the abuse Louis-Charles had endured. Once the autopsy was completed, the body was secretly buried in a mass grave at the nearby Sainte-Marguerite Cemetery.

But not all of the Dauphin’s body made it to the common pit. During the autopsy, Dr. Pellatan had slipped the wretched child’s heart into a handkerchief and placed it in his pocket. He was determined to someday return the relic to exiled members of the royal Bourbon family. (Louis-Charles’s last surviving immediate family member, Marie-Thérèse, sat unaware of his death in her cell on the floor above).

In the years following the secret burial, dozens of men claiming to be the Dauphin would come forward, many of them pestering Louis-Charles’s sister, Marie-Thérèse, the Duchesse d’Angoulême. Marie-Thérèse would be haunted by the mystery of what happened to her younger brother from the moment she was released from captivity in December 1795, to her death over five decades later.

Eventually over 100 people, most famously Charles-Guillaume Naundorff, would claim to be the real Dauphin. There were many practical reasons to make a claim. A Bourbon restoration was always a possibility, and a successful claimant could theoretically find himself on the throne of France. Riches, fame, and adulation also came to many imposters, thus encouraging others to come forward.

The charlatans were aided by the fact that in the child’s last days he had refused to speak, and no one who had known Louis-Charles in his happy youth ever saw him after he was brought to the prison. And of course, only Dr. Pellatan and a few of his friends knew of the pickled heart locked away in his desk drawer.

The heart of Prince Louis XVII. Manuel Litran/Paris Match/Getty Images

“There is no real and legal certainty that the son of Louis XVI is dead,” wrote the Austrian diplomat, Baron von Thugut. “His death, up to now, has no other proof than the announcement in the Moniteur, along with a report drawn up on the orders of the brigands of the Convention and by people whose deposition is based on the fact that they were presented with the body of a dead child who they were told was the son of Louis Capet.”

According to Cadbury, the mystery surrounding the “orphan of the tower” led to 500 books on the subject and an Edwardian-era monthly journal. The first book, a fictional account called The Cemetery of Madeline, about Louis-Charles’s supposed escape from the tower, came out only a few years after his death. Memoirs were also written by claimants themselves, including the Historical Account of the Life of Louis XVII, dictated by an illiterate, drunken vagabond named Charles de Navarre. Even Mark Twain got into the act, writing of a transient pretending to be “the little boy dolphin” in The Adventures of Huckleberry Finn.

The first claimant appeared in Châlons-sur-Marne only three years after the Dauphin’s death. The charming, handsome teenager had been found wandering the countryside and put in the local prison. For months he refused to say who he was, and then said he was a member of a non-existent ducal house. Enamored villagers became convinced the seemingly aristocratic young man was Louis-Charles, and the teen did not disabuse them of this notion.

Louis XVII being taken away from his mother, Marie Antoinette before her execution. DeAgostini/Getty Images

“Although still in prison, he was treated as a king,” Cadbury writes, “his cell luxuriously reappointed as a ‘little palace’ and a small ‘court’ organized with due pomp and ceremony…presents and money were lavished on him."

In due course, it was revealed that he was in fact a runaway and tailor’s son named Jean-Marie Hervagault. But this did not stop his courtiers from believing in his royal lineage. Hervagault's stories became more and more grandiose: The boy claimed that a brand on his leg, of the shield and the lilies of France, had been made by the Pope. He died in 1812, claiming to be the rightful King of France to the end.

In 1814, Napoleon’s fall led to a restoration of Bourbon rule. When the dead child’s uncle, Louis XVIII, assumed the throne, this led to a boom in men pretending to be the ill-fated Louis-Charles. By the mid-1820s, so many young men were claiming to be the Dauphin that doctors at asylums and bodyguards at royal palaces became adept at rebuffing them.

The fad made its way abroad, too. Fake Louis-Charles' appeared in England, Denmark, Columbia, and the Seychelles. In the United States, the most famous claimant was a Native American, Eleazer William, known as “Indian William.” According to Cadbury, he was eventually paid off by a French nobleman, and generously agreed to abdicate all rights to the throne.

Another man, calling himself Charles de Navarre, traveled to France from New Orleans and declared in court that he was none other than the lost Dauphin of France. Navarre, who was heavily scarred and missing many teeth, wrote pleading letters to the King and the Duchesse d’Angoulême, signed “Daufin Bourbon.”

Fraudulently claiming to be the king was illegal in France. Usually the authorities let it slide—but when imposters gained a following or made threats, they were arrested and put on trail to expose their lies. Charles de Navarre was arrested in 1817, and after a disastrous trial, sent to jail. He died there in 1822.

The Dauphin in the Temple prison. Universal History Archive/Getty Images

From Italy came the globe-trotting and dapper “Baron de Richemont.” He soon had his own court, wrote his memoirs, and began pestering Marie-Thérèse and others with elegantly written manifestos. When a confused Marie-Thérèse refused to respond, he began to write her menacing, threatening letters.

In 1834, the Baron de Richemont was put on trial. One day, a man rose in court and interrupted the proceedings. “I am the bearer of a letter for the gentlemen of the jury written by the real Charles-Louis de Bourbon, the son of Louis XVI,” exclaimed the man. He then produced a letter, which he claimed was from the true Dauphin, who would soon be known throughout Europe as Karl Wilhelm Naundorff.

The Baron de Richemont was jailed but managed to escape a year later. For years, sightings of the Baron would be whispered throughout France. But it was his rival, Naundorff, who would become the most believed of all the imposters.

Naundorff came from Prussia and claimed to be a clockmaker. In reality, he had been imprisoned in Germany for counterfeiting money (he had also been accused of arson). Much like another famous imposter, Anna Anderson (who later claimed to be Anastasia Romanov), he was unable to fluently speak his supposed native language.

Like Anderson, Naundorff soon convinced many people who had known and loved the real Louis-Charles, including his nurse, a Versailles ladies’ maid, his father’s private secretary and a former Minister of Justice, that he was the Dauphin. Many of these people wrote to the Duchesse d’Angoulême vouching for Naundorff and suspiciously insisting she give him part of her fortune.

As she had done occasionally in the past, the Duchesse d’Angoulême sent a trusted friend to inspect the claimant. The friend reported back that Naundorff looked like a Bourbon, had handwriting like a Bourbon, and seemed sane. “I am certain that my sister would recognize me after ten minutes’ talk,” Naundorff wrote. “I propose that she should meet me; I demand it of her.” Again, the tormented Duchesse did nothing.

Naundorff was eventually arrested and banished to England, where he founded a spiritual sect and got himself arrested for attempting to build a powerful bomb. He died in Holland in 1845. Both his gravestone and death certificate identified him as Louis-Charles. When his rival Baron de Richemont died in 1853, his headstone also claimed the long-dead boy’s name as his own.

Naundorff’s children and grandchildren continued to try and legitimize his claims, mounting court battles up until the 1950s. In the 1990s, scientists used a lock of Naundorff’s hair to prove once and for all that he was not the lost Dauphin.

Through the centuries, the real Louis-Charles’ heart had quietly gone on a remarkable journey. The hard, calcified heart had been rescued, stolen, trampled during a later revolution, and miraculously rescued again, ending up in the royal crypt of St-Denis, where Louis XVI and Marie Antoinette lay. In 2000, a group of geneticists proved definitively that it was the heart of ten-year old Louis-Charles de France. It is now encrypted with honor in St-Denis.