I would tell him and let him decide if he wants you as a client. I'd say "I wanna be honest about one thing. I know you from such a place and time, if it would be too awkward to meet up I understand. I am discreet though and wouldn't out you at all."
And on that subtext a recent provider and I in our post sex chat he mentioned that everyone in his family knows he escorts. So if it's the same for your guy for instance he totally might not care. 😅