may 31, 1740 - Coronation of Frederick II 'The Great'

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Frederick II (German: Friedrich; 24 January 1712 – 17 August 1786) was King of Prussia from 1740 until 1786, the longest reign of any Hohenzollern king. His most significant accomplishments during his reign included his military victories, his reorganization of Prussian armies, his patronage of the arts and the Enlightenment in Prussia, and his final success against great odds in the Seven Years' War.

Frederick was the last Hohenzollern monarch titled King in Prussia and declared himself King of Prussia after achieving full sovereignty for all historical Prussian lands.

https://en.wikipedia.org/wiki/Frederick_the_Great

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