How many french monarchs met death under the guillotine and for what reasons?

During the French Revolution, three monarchs met their deaths under the guillotine: King Louis XVI and his wife, Marie Antoinette, along with King Louis XVII, who died in prison. Louis XVI was executed in 1793 for treason after being accused of betraying the nation, while Marie Antoinette was executed later that year for similar charges, including accusations of conspiracy against the revolution. Louis XVII, the young son of Louis XVI and Marie Antoinette, died in captivity under harsh conditions, though his death was not a direct execution like that of his parents.