how do u know
But his hair isn't white though...?
Look at the demon lord in chapter 1.
He have white hair.
Then look at the 5th disciple in chapter 3, last page.
He have white hair too.
Now look at the man in black in chapter 8.
He also have white string of hair.
The last disciple is the reborn of demon lord. And he promise that he will be back for Lotie.
Its just my conclusion. I'm not sure. (⌒▽⌒)
and his magic is purple just like the demon lord *wink*
That man in black is the 5th disciple also known as demon lord.