William and his two half-brothers had the same mother, Harlette or Herleva of Falaise.  Of course, William’s father was Robert I, Duke of Normandy.  Harlette then married Herlevin de Conteville and gave birth to two sons, Odo and Robert.  While Odo was a cleric, he did father a son whose descendants included several noble lines.  William, his brother, Robert, and another Companion, Aimery, vicomte of Thouars, were the ancestors of many notable descendants including Henry II and his wife, Eleanor of Aquitaine, as well as their son, King John and his descendants.