Brother shows up out of the blue, kinda scared to meet him, what should I do?

I have a half brother on my dad's side, and since my dad is a complete douche bag I only ever saw my brother once when he was twelve and I was nine. Shortly after my sixteenth birthday on may 5th he sent me a message on facebook. We're talking and everything is great, but he wants to have lunch with me next week and I'm scared to meet him. I mean I haven't seen him in two million friggen years. What do I do when we meet? hat is appropriate to say? HALP