Complex sentence: William fitzOsbern (c.1020--February 22,1071), Seigneur de Breteuil, was a relative and close counsellor of William the Conqueror who became one of the great magnates of early Norman England.
Split into simpler sentences: William fitzOsbern (c.1020--February 22,1071), Seigneur de Breteuil, was a relative and close counsellor of William the Conqueror. William FitzOsbern who became one of the great magnates of early Norman England.