Question: Princess Frederica Dorothea "Louise" Philippine of Prussia, was a member of the House of Hohenzollern, and was a niece of which King of Prussia from 1740 until 1786, the longest reign of any Hohenzollern king?
Sentence (from "Frederick the Great"): Frederick was the last titled King in Prussia and declared himself King of Prussia after achieving full sovereignty for all historical Prussian lands.
Relevant evidence: No