Fürst von Nassau-Siegen, official titles: Fürst zu Nassau, Graf zu Katzenelnbogen, Vianden, Diez, Limburg und Bronkhorst, Herr zu Beilstein, Stirum, Wisch, Borculo, Lichtenvoorde und Wildenborch, Erbbannerherr des Herzogtums Geldern und der Grafschaft Zutphen, was since 1722 Fürst of Nassau-Siegen, a part of the County of Nassau.

[1] Frederick William became a ritmeester in the Dutch States Army on 23 November 1723, and colonel of a regiment infantry on 22 July 1728.

Thus, there were no male heirs and the Dowager Fürstin was compelled to accept that the Catholic Fürst William Hyacinth would take possession of the Reformed lands and the city of Siegen.

However, the Fürsten Christian of Nassau-Dillenburg and William Charles Henry Friso of Nassau-Diez also laid claim to the inheritance.

[14] In order to drive out this occupation by Nassau-Dillenburg and Nassau-Diez, Elector Clemens August of Cologne called in the Landesausschuß in his countries bordering the Siegerland.

On 20 August 1735, peasants from Cologne crossed the borders of the Principality of Nassau-Siegen and plundered "was ihnen vorkam" ("what was in front of them").

In the light of a strong flashlight one could see that in the niche of Frederick William is a coffin apparently made of mahogany, framed by gilt bands about 4 cm wide.