Fornication Under Consent of the King

Come across this piece of joke, don't really know how true it is, anyway just for a laugh...
In ancient England, people could not have sex without consent from the King. When people wanted to have a child, they had to solicit a permission to the monarchy, in turn they would supply a plaque to hang on their door when they had sexual relations.
The plaque read … "Fornication Under Consent of the King" (F.U.C.K.).
This is the origin of the word, agree? :p