I just thought of something that everyone else on this board probably thought of like a year ago- could Naruto be related to the fourth? They look tremendously alike, and they haven't revealed any infor about the fourth yet, so it is possible.. plus, I remember both Kakashi and the third saying something like "Sorry, fourth" during a discussion about Naruto, although that could just be because he sealed Kyubi in Naruto. Still, seemed like a possibility to me.