Slayertplsko

I would need to know whether GM rulers ever used the title král (kráľ, król, korol, király etc), a title later used in Hungary, which comes from the name of Charlemagne. Charlemagne was crowned by the pope, and Stephen I (the first king) was also sent a crown by pope Silverter II and Holy Roman Emperor Otto III, therefore the etymology of the word 'kráľ' is in Charlemagne's name.

Also, Svatopluk was mentioned as rex in Industriae tuae (880), the same title as the one the kings of Hungary were referred to, so I would like to know what latin word was used for his predecessors - Rastislav and Mojmír.

This title (kral) wasn't used (to my knowledge) earlier than 1000AD, or am I wrong at this point?