Unexpected Parentage Revelation

I found out I was result of my mom's affair with a school teacher I (26F) have older

brother (36M) and I always wondered why we had such a big age gap. I never had a reason

to get my blood group tested until I got pregnant. I got my blood group and I always assumed

I would be O+ because both my parents are O+. It wasnt and turns out I am A+ instead.

I confronted my mom and she denied and blamed me for accusing her of adultery.

I explained to her how I know and told her I will tell dad and brother if she doesnt tell

me. So she confessed after making me swear on my unborn child.

It was my brother's teacher who was also in school when I was. He never taught