i can already predict the sad outcomes for this
1.he learns the truth and is hurt then later on she either kills him, he kills himself or he is executed
2.he learns the truth and is hurt then later on she free's him from the duke and he wonders the world.
3.he learns the truth and is hurt then later he ether causes trouble for everyone and disappears or he kills the duke and disappears
4.he learns the truth and is hurt then later on ether tries to kill her or imprison her to witch he's ether crippled by the prince or killed
and finally, the one I hope happens is 5. he learns the truth and he helps her get back to the prince and she later frees him and they become allies/friends