Breaking the news to only child

Tosh
My son will be 7 when our new baby arrives. When I got remarried, he said he was fine with it "as long as there are no babies". He's made numerous comments that he dislikes babies and doesn't want a sibling- "his worst nightmare" he said 😑. I'm sure he will be fine with time, but I wanted to tell him in a way that made him feel special still. Anyways, anyone else had a similar experience? What ways have you used to break the news to them? I also wasn't sure if it would be best to wait until I had an ultrasound to show him? 
I guess this is what happens when you wait awhile between siblings!  Thanks in advance❤️