Horatio tilts his head, frowning deeply at this explanation. He's beginning to accept that this Doctor isn't Bush, that perhaps he's not related to him, and he's not sure that he's even close to being ready to ask about the man's species. Still, the explanation offered... doesn't quite sit comfortably with him.

"I would think, the infinity of the universe being what it is, it would be terribly unlikely for it to simply run out of ideas and begin re-using faces arbitrarily..." He stops, then shakes his head, still frowning, "...No, if not a blood relation there must be some way of accounting for it. Some shared condition... You'll simply have to tell me more about yourself, until we can discover what it is."

You'll just have to get to know him and be his replacement pal, Doctor. There's simply nothing else for it.