FYI, "thou" was the familiar or diminutive form of the more polite "you," (With the notable exception of "thou" being exclusively singular, leading to the Christian God being referred to as such to emphasize that there's only one of him) so it's a bit odd to translate Sol's fancy speak like that. In modern English what you've written would be equivalent to something like "Oh, so you're that Lord Bogart Rumholt, then?"
I'd focus more on the specific wording, with something like "You must be Lord Bogart Rumholt, if I be not mistaken?" rather than trying to get it across with purely word choice like the original Japanese does. The ways formality registers work in English and Japanese are just radically different, after all.