The pin was identified as belonging to the French queen when experts noticed the interlocking C's – for "Catherine."
Archeologists have found a lavish hairpin at Fontainebleau Palace, which they say belonged to 16th-century French Queen Catherine de Medici.
The rare 9 centimeter-pin was found by accident as the team was digging around a communal toilet to prepare the surrounding area for restoration.
This is the first time that a Renaissance royal possession has been found at the royal residence outside Paris.
The pin was identified as belonging to the French queen when experts noticed the interlocking C's - for "Catherine" engraved on it.
Fontainebleau Palace conservator Vincent Droguet also noted a finish of white and green, known to be Catherine's colors on the handicraft after he cleaned the age-old soil collected on it.
Experts cannot explain why the personal possession of a queen would end up in a Renaissance-era communal toilet.
"Maybe it was a lady-in-waiting who took it. Perhaps it was stolen, and just fell in," Droguet said calling the find a "mystery."
Catherine de Medici was Queen consort of France as the wife of King Henry II from 1547 to 1559.
She was notoriously devoted to diamonds and renowned across Europe for her lavish jewelry collection, much of which has been lost, sold or stolen over the centuries.