Question: When was the sister of Theodora Porphyrogenita died who was reigned as Byzantine Empress alongside her sister?
Sentence (from "Theodora Porphyrogenita (11th century)"): She was co-empress with her sister Zoë for two months in 1042 and sole empress regnant from 11 January 1055 to 31 August 1056.
Relevant evidence: Yes