That step-parent adoption/infidelity thing... S/O
What if it ISNT his kid? Like, he signs the papers and everything, but a DNA test would have shown it wasn't his kid, what happens then?
Hypothetical: she's pregnant and says it has to be his because she didn't have sex with anyone else, and he believes her. The kid is born normal and everything, and he signs the birth certificate, but it's really someone else's kid. No one does a DNA test, they just accept the kid as his.