Portrait of Louis XVII (top) and the heart of the child heir kept in a crystal vase. (AFP)

Paris, June 7 (AFP): One of the most intriguing mysteries in French history will be put to rest tomorrow when the heart of Louis XVII, child heir to the throne, is buried 209 years after his death in the royal crypt outside Paris.

European royals are expected to attend the funeral at the Saint-Denis basilica north of Paris, when the tiny organ kept in a crystal vase will be laid to rest near the remains of his parents, Louis XVI and Marie-Antoinette. Louis-Charles, the so-called “lost dauphin” who would have reigned as Louis XVII, died at the age of 10 on June 8, 1795 in the French capital’s Temple prison, with tuberculosis the official cause.

But his death has been the source of rumours and speculation for more than two centuries, with historians musing about the would-be king’s fate until DNA tests proved the heart belonged to a Hapsburg, like Marie-Antoinette. It’s no small wonder that the death led to controversy: Louis XVII’s heart was cut from his body, preserved, stolen, recovered and passed around for centuries before finding its way back to France.

Louis XVII was imprisoned with his parents and his sister in 1792 during the French Revolution. Once his parents were sent to the guillotine, Louis and his sister were separated, with the boy king confined to a cramped, windowless cell. Upon his death, the body of the child was ditched in a mass grave, but the doctor who performed the autopsy first cut out his heart and kept it in an alcohol-filled vase on his bookshelves. He boasted of his possession to one of his students, who swiped the prize. Years later, after the thief died of tuberculosis himself, his widow returned the heart to the doctor.

The physician tried for many years to return the heart to members of the Bourbon family but was thwarted by royal squabbles. Louis XVII’s remains finally found their way to the Spanish Bourbons, and eventually back to France.

Historians and conspiracy theorists seized on the amazing journey of the heart to argue that maybe it did not belong to Louis XVII after all, suggesting that instead of dying in prison, he had escaped or been spirited out of France to safety, and that the heart belonged to another child. In 2000, scientists conducted DNA tests to put the rumours to rest. Result: the heart indeed belonged to a descendant of Marie-Antoinette.

Those who wanted to keep the “lost dauphin” myth alive argued that the heart could belong to Louis-Xavier-Joseph, Louis XVII’s older brother who died in 1789. But the heart of the older brother had been properly embalmed according to royal custom, while that of Louis XVII had not. For historians, the debate was over.

“This is a way to give this child-martyr, who passed away in tragic circumstances and around whom mystery swirled for more than 200 years, a proper death,” said Charles-Emmanuel de Bourbon-Parme, one of Louis XVII’s relatives.