Man in the iron mask
Those theories that see the prisoner as part of the family of Louis XIV neglect that there was a lot of social control back then. The birth of a child in the court of the king, or even among nobles was a public event. Several hundred people were present at the birth of Louis XIV. The "secret birth" of a twin brother of Louis is highly unlikely. The amount of social control made it almost impossible that Anne of Austria had an affair. Anne was pregnant several times, which means that her husband, Louis XIII was able to father children. Another fact that speaks against the theory that the prisoner was a relative of the king is that the prisoner had the post of a servant, at times. At the times of Louis XIV, people of noble birth would not become servants.