The Man in The Iron Mask (1977)

Fed up with the the insufferably cruel behavior of Louis XIV, a group of musketeers plot to replace the king with his twin brother, Philippe. They kidnap Phillipe and temporarily lock him in the Bastille, where he is inevitably recognized as a dead ringer for Louis. Word gets back to the king and, fearing for his safety, he decides to have his brother locked in an iron mask and imprisoned for life.