Complex sentence: Sellar suggested that this tradition may have derived from a garbled version of reality; perhaps, Sellar argued, his mother was daughter of William fitz Duncan, another famous Earl of Moray, but from the twelfth-rather than the fourteenth-century.
Split into simpler sentences: Sellar suggested that this tradition may have derived from a garbled version of reality. The latter was another famous Earl of Moray, but one who lived in the twelfth-rather than the fourteenth-century.