That's a good question. We don't have rent control here (thank goodness), but I would suppose the answer would depend on a couple things: When you added him, is he listed as a tenant, or only a temporary caretaker for the tenant; and was he made to be responsible for the rent (jointly & severally liable as co-tenants are)? I would suggest you call whoever governs rent control in your area and ask. If he is now eligible, you may be stuck with that low rent amount for the rest of his life. On rent control units, always raise rent the max each year. (Yes, I know she was elderly and you gave her a break.) But if he can take over on her amount, that break may come back to bite you for years to come. Do call the agency that governs rent control and find out.