What would you do if you saw your Doppelgänger in person?

I have seen a doppelgänger in real life impostering my long time friend whom I haven't seen for a decade and on other occasions looks like her tenants daughter, then a chubby teenager and so on, like showing off that she could do all that but what's funny is that she forgot that she's always with her son and husband that is why always laugh everytime I remember those moments.

If ever this happened to you, what would you do? Will you confront the person or just let it be?

I would confront them, and ask them to fill in for me at work.

I have the answer,in fact I only read the book earlier this year,not sure if you are into literature or not but I am,in particular one Russian writer whom I love dearly,I have all his books, the book is "The Double" by Fedor Dostoyevsky, it is a brilliant read,some of his other books you would of heard of for sure,or seen them as movies,namely "The Brothers Karamazov" or his classic "Crime and Punishment",and "Notes From Underground" the lesser known but my favourite is his book "The House Of The Dead",but the Double should really interest you!
I will try put a link to a good preview.

http://thelectern.blogspot.com.au/2008/12/double-dosteoevsky.html