Okay, so here's the scenario in the film I had watched, let me know what you guys think should have been done.
The story is set during the crusades. The king of jerusalem is peace loving, and on good terms with Salah AlDeen. Only problem is, he has a disease, and will die in a very short amount of time. The person who will inherit the throne is his sister, sybilla. She is married to an evil, war hungry, horrible man. And then there's this other guy, Balian, your typical movie hero, a knight, honorable, honest, etc. The king asks Balian to marry his sister, so that when he dies, Balian will be king, and not the current husband. But the husband must be "gotten rid of" before he can marry the sister. Even though he is a vile person, he is still technically innocent of any crime. So what happens is either this:
1-Balian refuses, and the evil man becomes king. He breaks the truce with Salah AlDin, goes to war, and has thousands of people killed, and eventually loses jerusalem.
2-Balian accepts, the evil man is executed (this is the little evil), Balian becomes king, jerusalem stays on good terms with Salah AlDin, they work something out, there is no war, and no one is killed.
What happens in the movie (and history, of course), is the first case. If you had been Balian, what would you have done?