Complex sentence: Therefore, Sido is not the daughter of the Marquis, but of Isabelle and Armand; the pair had been attempting to elope to London with a three-year-old Sido at the time of their murder.
Split into simpler sentences: Therefore, Sido is not the daughter of the Marquis, but of Isabelle and Armand. The pair had been attempting to elope to London with a three-year-old Sido at the time of their murder.