The personal union of Prussia and Poland went through many iterations in terms of what flags should be used in Prussia, Poland, and internationally for the two nations. However, with the King of Prussia and Poland becoming enamored of the writings of the Dane, Zeus Korsgaard, he saw himself as the embodiment of the state, and sought to knit the two nations into a Korsgaardian-style Empire. Persuant to that, he ordered the commissioning of a new flag for the Empire of Prussia-Poland, incorporating the colors and symbols of the two and of empire.
Flag of the Empire of Prussia-Poland
My cameo strikes again Make the family proud Zeus!