Certainly any new encroachment is not covered. In addition, this may be more akin to a prescriptive easement which requires 20 years. There are not enough facts here to know which may actually apply.
I suggest you immediately seek the advice of counsel knowledgeable in the areas of adverse possession and prescriptive easements to determine which might apply and what you may be able to do to resolve this issue. Based upon timing, they may suggest you immediately give the neighbor a "license" to use that portion of the property (revokable at will) so that you can effectively stop the use. Or, if adverse possession can be claimed, there may be other tactics to follow.
Land in Alexandria is valuable. Given the number of years involved you should act immediately to preserve your ownership.
Please note that this response is based upon the limited information available in the question. In addition, it is not intended to create an attorney/client relationship and is offered only as general information and not as legal advice.