I took the end with a grain of salt, because how would you explain Isshin and Ichigo having similar naming Zanpaktous and both having the ability Getsuga Tensho, him calling Ichigo son could be a elder talking to a youngster thing he could even be his grandfather.
This might also explain what Aizen has to do with this, because if you remember when him a Ichigo were fighting Aizen said "I have been aware of you since the time you were born" he then says "Since the moment of your birth you have been special....because you are the offspring of a shinigami and" at this point Isshin shows up and tells Aizen he talks to much.
Also in the next chapter when Isshin takes Ichigo out of Aizens way, Aizen says "Keep your distance...a fast and wise decision...seems it runs in the family". I take it he was talking about Juhabach.
KT really is the ultimate troll but we can't say he didn't hint at all this.