Nathan is Templeton's go-to man in the matter of quietly disposing of Princess Victoria. He was the head of her New York security detail, and responsible for having her in place for her 'accident'. Unfortunately for him, Gerard, her former bodyguard and still friend, got wind of the plot, and enlisted his old chum Christopher Chance to help spirit the Princess out of harm's way. With the fall of Templeton, Nathan presumably ended up serving prison time also.
While searching for Princess Victoria he calls out "Your Majesty?", whereas, of course, if formality were appropriate, "Your Highness?" would be the correct form of address. More likely, a simple "Ma'am?" or similar would suffice.