Merlin and Arthur, a Different Ending

What if you could change your destiny? One person's choice changes everything, the present and the future. The fate of this man has been written since the dawn of time. What will change if a single choice saves him, when the story we all know told us he was supposed to die?

This is a Merlin fanfiction!
I'm sorry about the description, I really have no idea what this story is about yet.