It’s *still* your original idea though. Consider it this way: You came up with it on your own. The fact that someone else *happened* to _also_ have the same notion doesn’t make it any less original. It originated from _you_.. and *also* from them.. but that it came from them as well, does not take away from it coming from you.
Also, look up the guy who came up with it. That you BOTH came up with the _same idea_ independently of each other speaks volumes.