What are the chances of your best friend and you being cousins?

I don't know what the chances are of this happening, but I started working with this girl, when became really good friends and then we started a realtionship I was indtroduced to her second cousins from her maternal (mother's) side of the family, but when I was indroduced to her second cousin's, I knew that they were my paternal (father's) side of the family. Even though me and girlfriend are not cousins, its funny we shared the same second cousins and ever met before, so I guess there may be a chance that your best friend and you are cousins.