"Dirk V (1052 – June 17, 1091) was Count of Holland (called Frisia at that time) from 1061 to 1091.
Dirk V succeeded his father, Floris I, ...
under the guardianship of his mother, Gertrude of Saxony. William I, Bishop of Utrecht, took advantage of the young ruler, occupying territory that he had claimed in Holland. William's claim was confirmed by two charters of the emperor Henry IV. (April 30, 1064 and May 2, 1064). Dirk only retained possession of lands west of the Vlie and around the mouths of the Rhine.
Gertrude and her son withdrew to the islands of Frisia (Zeeland), leaving William to occupy the disputed lands. In 1063 Gertrude married Robert of Flanders (Robert the Frisian), the second son of Baldwin V of Flanders. Baldwin gave Dirk the Imperial Flanders as an appanage - including the islands of Frisia west of the Frisian Scheldt river. Robert then became his stepson's guardian, gaining control of the islands east of the Scheldt. Robert managed to conquer Kennemerland (north of North Holland), but held it only briefly." - (en.wikipedia.org 10.04.2021)
