Mother got pregnant

My mother 38 widowed at 33 and didn't date after being widowed. I was shocked hearing was pregnant wondered by whom. At 22 I was living at home and going to the local university and my mother was always home and never went out at night. So, her getting pregnant was a bit of a shock and IVF thought she had used IVF and secretly stored my late father's sperm. No, she hadn't, my father was 20 years older than my mother and I was the result of a short fling and because she had gotten pregnant, they had married. Mainly because of her age at the time, 15 at the time of the fling and to avoid prison he married her. His family is very well off, and my father played the perfect father. But wasn't really around all that much, his older brother's son was, and he and my mother became very close. Lovers and had to keep their relationship secret, after the death of my father. They wanted to public as they say, but sister of the 2 now departed brothers told them no. She herself passed earlier last year and as the saying goes our time had come, but waiting until legal requirements were settled before marrying. Yes, they married just 3 people and the minster on the first of December 2023. No cousins left and it's just us 3 and the baby brother my mother is carrying.