film which name i don't know

Everyone knows it when you saw a film like 5 years ago and you want to see it again but you don't know the name of the film and the actors. I hope that there is someone here who can help me.

the guy i call leader is the leader/king of the city i am not sure what his name is but i think it could be amun or something similair to it.

It is about a scifi film .
the scenes that I remember are:
that there is a king/leader of a city, like in the first hour his wife gives birth to 2 children a boy and a daughter. And his wife dies. Later he went into the city and there was a thing that is called a fire titan(or something like that) and the companion/the guy who walks with the leader said to him: do not look to the fire titan, but still the king looked and he became blind.

And after there is someone called Duncan who has to gaurd te leader but is actually an assassin who has to kill the leader( it was a mission given to him by someone who's name i don't know) and when the leader was by her wife who died atm duncan came in the room he wanted to kill him but he decided to don't kill the leader.

there is also a other women (probabl the sister of the leader or the sister of his wife) who took the leadership when the leader dissapeared( i dont know why he left the city) asked duncan to stay with her when the son and daughter of the leader left the city ( this was when they grew up and had an age around the 16, and btw they did not left the city with their father)

the last scene i remember is that duncan walks to a door of the palace in the city and he saw the sister of the leader having sex with one of the counselers/advisers of the leaders. He felt betrayed and almost took his knife but he kept hid head cool and walked away without letting the sister noticing him. And the reason why she had sex with the counselor/adviser becuase he wanted to help her with a task.
The task was to get rid of a old man who was preaching things and in fact this was actually the leader of the city who returned but nobody knewed it was him.


the rest of the film i can't really remember that good. I hope there is someone out there who could help me:) and already tx for ansewring my question and putting effort in it if help:)(and sorry for bad english i am not a native speaker)