Robert I, Duke of Normandy

Robert I was the father of William the Conqueror.

William was the son of Robert and Heleva and was illegitimate. Heleva married Herluin de Conteville as she had been promised in marriage they had two sons that were the half bothers of William I. Odo (Bishop Odo) and Robert (Count of Mortain)

Robert was also the father of Adelaide of Normandy (Adeliza) either by Heleva or by another "concubine" (the Wikipedia page is not clear).

The value of Wikipedia

While Wikpedia is a great starting point and when facts are well established there are more than a few authors that are willing to expand on them. However, when the opposite is true the Wikipedia pages are not as useful. The Normans before Conquest is a case in point.