'Medieval Times' SUED -- I Got Royally Screwed ... Claims Former King

Hear ye, hear ye ... a King who once resided over Medieval Times in California claimeth he's been screwed out of his royal sum -- and now he wants what's coming to him.

King Scott Ehredt -- ruler from 2008 A.D. - 2013 A.D. (at the chain's popular Buena Park location) -- allegeth he was paid a less than royal amount to film a "Medieval Times" ad campaign in '11 ... even though his court was paid much more.

Your majesty sayeth non-employee actors on the shoot told him they were paid "thousands" for the campaign -- however he merely received $18 an hour ... peasants pay!

A rep for Medieval Times telleth TMZ they deny the allegations.

King Scott of Buena Park bids the judge for restitution to be determined at a later date ... as well as compensation for damages incurred.

... or they could just battle to the death in the Medieval Times arena.