Le Secret du Masque de fer (The Secret of the Iron mask) is a historical essay by French novelist Marcel Pagnol, who identified the famous prisoner in the iron mask as the twin brother of Louis XIV, born after him and imprisoned for life in 1669 for having conspired against the King. The essay was published for the first time in 1965 under the title Le Masque de fer (The Iron Mask), and updated in 1973, completed in particular with research on James de la Cloche, identified as the twin bearing this name in his youth.