Well...I don't know if I would react any differently, but I can relate a story, not exactly the same, but it may be interesting.
In my family there are 5 boys: me being the eldest.
When I was a teenager, I found out I had 2 older half-brothers. My mother had a son before I was born; he was raised with my grandmother, but we were told he was our uncle.
My father, had a son also, but didn't live anywhere near us. He lived with his mother in southern Ontario.
In 1984, I wanted to find out more about this 'brother' I had. So I placed an ad in the local paper. I received 3 replies. I met 1 family, but obviously they were not the same. I had one letter, but it was not even close to the information I had. Then I got another letter, and bang on! it was him. He knew who his father was (named my father's full name and more information).
We arranged to meet. It was very odd. Here is someone who looks vaguely like the rest of my family, but he was 24, I was 21. Never met before. We spoke on the phone. Eventually, I take the train down to meet with him.
Honestly, it was like starting from scratch.
It's a long story, but well...anything is possible.
I wish you nothing but the best with your first encounter.
Will you have anyone with you? friend, family member, wife ? I would highly recommend it at first. (Meeting Day)
You two can catch up (you and Dad) privately a bit later. You'll need that.
Best wishes, and please, please come back and let us know how things turned out, will you?
Thanks! It'll be an incredible experience, I'm sure.