Amy: Come on, okay, how can--how can you both be real?
The Doctor-Ganger: Well, because... we are. I'm the Doctor.
The Doctor: Yeah, and so am I. We both contain the knowledge of over 900 years of memory. And it's apparent we both wear the same bow-tie, which is cool.
The Doctor-Ganger: Because bow-ties are...
The Doctor: ...and always will be.