gender reveal

Kate
This is my 3rd pregnancy. 1 healthy 2 year old baby girl and I had a miscarriage in July 2016. We are now 16weeks and pregnancy seems to be going fine. I feel totally different with this pregnancy than I did my first. This will be our last baby no matter what, and I don't want to find out the sex, but my fiancé does. He cannot wait and just let it be a surprise at birth. We go to the specialist in 2 weeks to have an ultrasound and they could tell us the gender. How can he know and not tell me? I will be able to tell by his reaction. I really don't want to know! Anyone else go through anything like this?