Older son dislikes new baby

So today I realized, my 8 year old son, soon to be 9 next month, is not thrilled to become an older brother. I asked him if he wanted to feel the baby kick and he just didn't want to come near me. Then I asked him if he was ok with the idea of a new baby and he said no. I know that he's probably afraid of change. He's been the only child for all of his young life and now, I'm bringing in a new kid into his territory. I get it. I joked and let him know that nothing would change, he's still get yelled at just the same. To which he laughed because he knew I was kidding. But it still saddens me to see my son feel like he'll be replaced or that things will change. I know that in the beginning things will be different because of the attention the baby will need and will get from everyone, but other than that, I will always keep in mind to give him his due attention as well. What can I do to make him feel like this isn't then end of the world for him? Have any new mom's with a big age gap had this concern or issue with their older children? My son is from my first marriage and now I'm having a baby with my second husband. Any advice would help. TIA!