When Monmouth was a little boy, one of his tutors, Thomas Ross, encouraged him to believe that his parents had been secretly married. Â The tutor was removed once Charles realized what he was doing, but the damage was done. Â Monmouth sincerely believed that his parents had been secretly married, and, unfortunately, he was encouraged to do so by politicians who were desperate to prevent James from coming to the throne. Â
James believed that Monmouth's real father was a man named Robert Sidney: Â "The knowing world, as well as myself had many convincing proofs to think he was not the king's son but Robert Sydney's. Â After her being with the King, she proved so soon with child, and came so near the time, that the world had cause to doubt whose son Monmouth was. Â When he grew a man he proved the likest thing I ever saw, even to a very wart on his face." Â
Source: "King Monmouth" by Allen Fea