This seems to be the confrontation between a king and a saint-to-be, it might be Saint Gregory the Illuminator - during his meeting with King Trdat. If so, this is what the Wikipedia has on it: "Educated in Caesarea in Cappadocia by a Christian nobleman Euthalius, Gregory sought, when he came to man's estate, to introduce the Christian doctrine into his native land. At that time Tiridates III, a son of king Chosroes, sat on the throne. Influenced partly by the fact that Gregory was the son of his father's enemy, he subjected him to much cruel usage, and imprisoned him for fourteen years. It would be useless to recount the various forms of torture which the orthodox accounts represent the saint to have endured without permanent hurt; almost any one of his twelve trials would have been certain death to an ordinary mortal. But vengeance and madness fell upon the king, and at length Gregory was called forth from his pit to restore his royal persecutor to reason, by virtue of Gregory's saintly intercession."

I feel I'm on solid ground as the fresco is next to another scene, of the saint being hung upside down.