Question: What is the cause of death of Theophano Of Athens's husband?
Sentence (from "Staurakios"): However, due to these injuries his reign was short, he was usurped by his brother-in-law, Michael I Rangabe, on 2 October 811, after which he was sent to live in a monastery, where he stayed until he died of gangrene on 11 January 812.
Relevant evidence: Yes