As much as I love The Flash TV series and yes I'll probably get hate for this. If you are not up to date please don't continue reading this.
Spoiler from season one.
At the end of season one we saw Eddie shoot himself to stop The Reverse Flash (Eobard Thawne). Because Thawne is related to him, so he disappeared.
Now theoretically, if I went back in time and killed my great great great great grandfather then i would never have existed. So if Eddie died, Eobard would never have been born. If he was never there Barry's mom would never of been killed so he would never have been a forensic scientist and would never have been struck by lightning so he would never have become The Flash.
Now, by rights there can only be one explanation for this and still work. If this was all planned and Thawne was just saying he was from his blood line knowing he'd kill himself and he is just hiding, OR that he is actually Eobard Thawne the one from earth two and he killed earth two Eobard.
Thanks for reading and if you think they have stuffed up somewhere feel free to add that in the comments :).