Answer:
That Madeline is dead
Explanation:
He clearly states that he has been informed of Madeline Usher's fate abruptly as you can read yourself taken directly from "Fall of the house of Usher" as it follows:
"I could not help thinking of the wild ritual of this work, and of its probable influence upon the hypochondriac, when, one evening, having informed me abruptly that the lady Madeline was no more,"
