From 1513 to 1972, the Danish Kings were named Christian, Frederick, Christian, Frederick, Christian, Frederick, Christian, Frederick, Christian, Frederick, Christian, Frederick, Christian, Frederick, Christian, Frederick, Christian, Frederick (it ended with the current monarch Margrethe, a Queen). – WTF Fun Facts
Source: https://en.wikipedia.org/wiki/List_of_Danish_monarchs
Until the late 60’s the Danes did not have a written language. Each generation having forgot his grandfathers name had already been used.
Well, the kings of prussia were all named Friedrich, Wilhelm or Friedrich Wilhelm…
Naming the sons after their fathers can be confusing…