He may be her father, but you're her Dad. He does have genius timing. He tells just after the age where he'd need to pay child support.

Among the many tragic aspects of this story, is that if ed5509 really loves and cares for his daughter, he needs to press for a paternity test, getting a DNA sample from the man claiming to be the father via court order, if necessary. That's because, even with today's technology, there is a non-zero chance that knowing the paternal family of origin will help doctors be on the lookout for certain diseases, and in the event an organ donor is needed, it (on average) doubles the pool of potential donors. In addition, the way medical technology is heading, it seems likely that some advances in the future are going to rely on as complete DNA information as possible, which would include not just the patient's DNA, but also that of their parents and maybe even grandparents. It's like, "Screw you, the moment I know I won't need to pay anything, I'm going to detonate a nuclear bomb in your life just for the fun of it, and to keep your daughter as healthy and as safe as you can, you can't even ignore me or ignore the issue." The guy sounds like a psychopath.

DNA doesn’t make a family, you’re her father in every way

I would leave her man. You do not deserve that. So she had an affair with this douche nozzle, and apparently is still in communication with him behind your back? Look, she thinks this guy is the dad, but instead of approaching you about the mistake, she sends him pictures behind your back? You should leave asap, and give yourself time to heal. This does not mean you should not be in your daughters life (blood does not make family) but this is heavy. Good luck to you.