Telling older child!

I am 35 my only child is almost 10, and I want a great way to tell him he is going to have a baby in the house! He stopped asking me around 6 or 7 if I was going to have another baby, I guess he gave up. I don't want some t-shirt etc, I want something grand! He will be so excited! He has siblings on his dad's side but has always wanted a live in sibling if you know what I mean. So if you have any great ideas I would love to hear them. We won't tell him until we are sure everything is a-ok!  Estimated due date nov 21st.