Aberforth Dumbledore and his elder brother Albus Dumbledore had a severe disagreement and fight after the latter was blamed for being the cause of their sister Ariana's death by Aberforth. While Albus Dumbledore and Gellert Grindelwald had become very close friends, Abeforth disapproved of Gellert's views, causing for a duel to breakout between the two. Ariana tried to intervene, and Albus tried to intervene too, and in the resulting wand waving, one of the curses hit Ariana, and she died.