Who is the Last Cylon?

Thinking logically now. Consider the following:

The Xena Cylon said that the last Cylon is not in the fleet. How would she know that. Does she know what all 36,000 people in the fleet look like? Not likely.

So, I believe that she must know the wherabouts of this last Cylon.

Sometime in last season, a person excaped from the Cylons and found the fleet. Could there be others like him. Quite likely, I think.

There must be someone still on that very same Cylon base ship that is in captivity there. I believe that this is the last cylon.

But who is it?

One of the other Cylons once claimed that "Adama is a Cylon". There are three Adamas. One is dead - Zach, having been killed somehow before the series started. We have never met him. He was killed in some sort of accident or something in one of the vipers, I believe. We know that people can get blown up, yet live (Starbuck). Could this have happened to Zach as well? And, could he have come back to the Cylons and be captured by them?

I think Zach is the guy. He has "been with us since the beginning" (sortof). The only question is his origin. He would have to have been adopted by the Adama's or something.

Of course, Xena might just be going on some sort of vision she had. I hope it isn't that, though.