Oh, my!
I bet you have a ton of interesting paternity stories!
I have a few, and I didn't even work in the field. They just kind of fell into my lap.
My ex husband thought he was going to be a father (we were already divorced, this isn't related to our break up). It was a one night stand and the woman told him it could be someone else's, but he stuck by her anyway until they could test the baby. The whole pregnancy, he was supporting her, taking her to prenatal appointments, and giving her money. He kept asking where the other potential father was. Why wasn't he helping, showing up, etc. She wouldn't give him an answer. His mother even through her a baby shower. After the baby was born, and they were waiting for the test results, the other prospective father still wasn't in the picture, and the ex kept asking, where is this guy? His mother grew really attached to baby, it was her first grandkid.
Turned out the baby wasn't my ex's.
It was her stepfather's. He was in the picture the whole time, hiding in plain sight, as grandpa.