Complex sentence: The seat of Pope Cyril VI during his papacy was in Saint Mark's Coptic Orthodox Cathedral in Azbakeya in Cairo but he built the Saint Mark's Coptic Orthodox Cathedral in Abbasseya, also in Cairo, which then became the Seat of the Coptic Orthodox Pope.
Split into simpler sentences: The Seat of Pope Cyril VI was initially located in Saint Mark's Coptic Orthodox Cathedral in Azbakeya, Cairo. However, during his papacy he built the Saint Mark's Coptic Orthodox Cathedral in Abbasseya, also in Cairo, which then became the Seat of the Coptic Orthodox Pope.