"DO NOT KILL THE DRAGONRIDER UNTIL YOU HAVE TAKEN MASTERLESS GLENCOUR UP TO THE VERY TOP OF THE STAIRWAYS TO KILL THE OLD DRAGONSLAYER BOSS IN THE CATHEDRAL OF BLUE!!!"

https://www.ign.com/wikis/dark-souls-2/Heides_Tower_of_Flame

Pfft! What do I look like, smart!? :) I finally get to the cathedral and face off against one out of a certain duo...