This question already has an answer here:
Ironically, take a look at this question:
Why does the header of a closed duplicate question say "Possible Duplicate:" when the footer says "Closed as exact duplicate"? If the question gets the 5 votes and is closed, can we change the header to say "Exact Duplicate:" instead? It's a little confusing the way it is right now.
Either that, or include the link the the duplicate question in the footer. For example: "Closed as exact duplicate of [link] by [....]".