It's not about who killed Arundel. It's the one who defeated him. Since Thirteen was the one that orchestrated everything, the right to replace him in the Order was Thirteen.
Thanks for the chapter.
btw author in yesterday release the was a note that two more chapter in 2hrs. was that a mistake.
Excuse, this peasant for asking more than what i deserve that too for free, but i am an addict.