Kaiser Wilhelm II/ Hohenzollerns' net worth c. 1914

Hi all, wondering if anyone knows of where I could find information relating to how much wealthy was the German royal family in the early 20th century?
 
Jahrbücher des Vermögens und Einkommens der Millionäre (almanacs of capital and income of the millionaries), 20 Volumes, published by Rudolf Martin, 1912/13.
 
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