This was beginning to become tedious. He had thought that Aberforth would at least give him a bit more of a fight, he had imagined that the old man's sense of self preservation, his thirst for life would allow him to fight. But perhaps he was simply too old, or perhaps even the thought of joining his brother and sister in the hereafter was much more appealing to him than Voldemort had guessed. He had wanted the old man to hurt, to be able to have the final duel with him that he had missed out on with the other Dumbledore bane of his existence. One did as they must in these situations though, and as much as the idea of cutting out his tongue appealed to Voldemort, it was time that this came to an end.
That didn't mean that there couldn't still be a bit of entertainment for them. They had, after all, come all the way out here.
The Dark Lord purposefully met Aberforth's gaze, no emotion present on his pale face. "You are the one who was careless Aberforth. Did you think I would never find out about this? Children speak, and you were a fool to trust them. Open defiance of the new order carries a stiff penalty old man." But first, he wanted him to see what was to become of his beloved sister, to make him watch as the image of the girl he loved died all over again. He turned again to the portrait, releasing the charm that had held her stationary and called out, Incendio!. The flames burned an immediate bright white, and burned only the portrait itself, starting at first the bottom edges and slowly moving up to consume the lone figure therein. He could see the girls fear as the fire moved toward her and knew that the sentient being could feel the heat, and with it every lick of the fire as it consumed her.
Turning back to Aberforth, Voldemort said nothing else to him and turned a deaf ear to any pleas or any final offensive words, then simply pointed his wand at the man and commanded loudly, "Avada Kedavra!."