The Diary Of The Fourth Friend Of The Golden Four

I am certain that every wizard, every witch and nearly every muggle has heard about the Golden Trio. Harry Potter, Hermione Granger and Ron Wesley. They are famous, I know. After all, they fought Voldemort and they eventually managed to kill him. So, they basically saved the world, the magical and the not magical.
But during all that bustle, except that Dumbledore is not so "light" and Voldemort is not so "dark:" and one important factor shouldn't be left out.
This might seem confusing, regarding that you probably believe to know the entire story. But let me tell you: you don't. Believe me! (Unless you've read my diary, but we'll get to that later!) That's why you might ask yourself what that factor is. The game-changer.
Well, to cut it short: It's me, and this is my diary.