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Following the death of Duke Bolesław III Wrymouth in 1138, as specified by his testament, the Masovian province was governed by his second son Bolesław IV the Curly, who, after he had expelled his elder half-brother Władysław II, in 1146 became Grand Prince (High Duke) of Poland. His Masovian realm also comprised the adjacent lands of Kujawy (Kuyavia) on the west bank of the Vistula.