Complex sentence: The assassin, an Alan, employed by her, is said to have wounded Illus; but this is doubtful, as historians have confounded her plot with the later one of her daughter Ariadne.
Split into simpler sentences: The assassin, an Alan, employed by her, is said to have wounded Illus. However, this is doubtful, because historians have confounded her plot with a later one by her daughter Ariadne.