A monarchy is ruled by a King, even if he's called "Pope"
Many do not realize this but the state, Vatican, is a monarchy state-confirmed by Vatican's State Department: "Vatican City State is governed as an absolute monarchy. The Head of State is the Pope who holds full legislative, executive and judicial powers." So if a state is a monarchy, and the ruler of that state is the Pope, that by definition means he is a King. The world who calls the ruler of Vatican-Pope, is biblically and technically known as King.