When the inheritance came to Hessen-Kassel technically Frederick I was sovereign there. But he had become King of Sweden, and so had placed his younger Brother William VIII in charge of the Landgraviate. Frederick I waived his inheritance of Hanau-Münzenberg in favour of his younger brother. So Wilhelm VIII became Count of Hanau-Münzenberg in his own right. In 1751 King Frederick died and William VIII succeeded him as Landgrave in Kassel. The next heir, Frederick II had secretly become Roman Catholic. When his father received this news finally he was not amused at all: He tried to secure that Frederick II couldn't change the confession of his lands in any thinkable way. One measure he took was to make Hanau-Münzenberg a secundogeniture of Hesse-Cassel known as Hesse-Hanau, and transfer it immediately to his grandson, William IX. William, still a minor when his grandfather died was put under the guardianship of his mother, Princess Mary of Great Britain, a daughter of King George II of Great Britain, excluding her Roman Catholic husband. So Hesse-Hanau was governed by Princess Mary from 1760 to 1764 and afterward by her son William IX. Only in 1785 he succeeded in Hessen-Kassel. So for nearly half a century after the acquisition of Hanau-Münzenberg by Hessen-Kassel in 1736 it stayed a separate most of the time. Only from 1786 on the integration into the Landgraviate took place gradually.Dietrich, pp. 208–211
