Officials said it's the first time in living history that a possession of the Renaissance royal has been found at Fontainebleau Palace.
The 3.5 inch pin was identified because it bore the initial “C” and the white and green finish known to be Catherine's colors.
The rare artifact was found in a toilet waste receptacle. It was discovered as the communal facility was being prepared for restoration work.
Conservator Vincent Droguet said the pin's location was “a great mystery.”
He added, “Perhaps it was stolen, and just fell in.”