Is there suddenly someone in your life that looks a lot like you, shares the same (or a very similar) name, and is slightly different? To any one who interacted with an extended family this isn't anything new. This is just cousin Sam at the family reunion. Sharing a face with a stranger is pretty much expected.
An interesting twist would be most of the crew being freaked out but the one character from a large family just shrugged it off, decides on alternating names and starts calling his/her double 'cousin'.