Heart of the Dauphin

Contained in a crystal jar in the crypt of the Bourbons in the bottom of the Basilica of Saint-Denis just north of Paris, the small withered heart is kept as a relic of Louis XVII, who died mysteriously in the French Revolution.

After his father, Louis XVI, was beheaded at the guillotine in the Reign of Terror, the young dauphin, who was kept in the Temple Prison away from his mother Marie Antoinette, was only briefly the official king, and of course never crowned. It's believed he died in 1795, but it was only years later, and after several impostors attempted to claim his identity, that it was proven. The heart was sliced out by a surgeon the day after Louis XVII's death and passed around for years, the alcohol it was submerged in eventually evaporating and leaving just the mummified heart.

It arrived at the basilica in 1975. The basilica itself has long been the burial place for the French monarchy, although during the Revolution all of the tombs were opened and their contents tossed into a couple of mass graves. These tangled bones have since been moved to an ossuary in the same crypt where the dauphin's heart is on display. 

Nearby, the remains of the dauphin's parents, Louis XVII and Marie Antoinette, are interred beneath slabs of marble. (There was really not much left of the guillotined corpses as they'd been buried under quicklime, but the bones and bits of grey matter and a lady's garter belt were later collected when the Bourbons briefly returned to power in France.) A DNA test with a lock of Marie Antoinette's hair definitively proved that the heart was of someone related to her, and now the preserved organ is kept beneath a cenotaph showing the dauphin's young face and curly hair.