I mistakenly added a friend, and now I cant delete the friend! WHY?

I got a friend invitation for a william f and without thinking I hit accept, after looking through his/her profile I realized that I didnt know this person so I went to delete him/her and It says that "this person is not connected to you on 360", but the "friend" william f shows up in my friends list. Why? How can I get rid of this friend?