The concept of "Divine Right" is really more of a 17th century concept, not Medieval.
Perth beat me to it.
Getting more technical, Medieval rulers ruled by raw force, but governed by church approval. That is, they became king because they had the biggest army: but they led a nation by staying on good terms with the church. Obviously, BM isn't exactly like that; it's not much like that at all (SA isn't even close to that level of independent power), but the principle remains.
