Wait I don't understand. She is his niece but he said he's the dad? I know I'm stupid but ...

I think on paper and every way recorded he is but actually he isn't but no one knows so if u only go by things that stand on paper he would be. As only it seems him, babygirl and now her knwo the truth (dk thats what I understood)(￣∇￣")

I think it’s for looks and just so other families don’t view them a certain way since she’s not his actual daughter. He’s her uncle and she’s his niece.

Maybe he has a reason to keep it hidden, like for example if he has many greedy relatives and doesn't want them to show up and challenge his adopted daughter's inheritance rights in the future... or even if she's some dead sister of his' illegitimate baby that he took in, and he wants to protect his niece from the social stigma...

It doesn't matter if he's her uncle or dad what matters is, he is raising her with love and taking care of her so what if he inst her biological father he is still and forever will be the father that raised her

Of course, to most of the adults it shouldn't matter, but to the mc it might be important up to some point, if it helps her understand the lil girl better so they can keep getting along... which might be necessary if it's something the lil girl still hasn't been able to come to terms, with and there might be a good reason for that (like, for one, if she was previously with her real dad it'd be hard for her to call someone else "dad", even if it is just in front of strangers so as to avoid problems...), but whatever the reason the mc as her nanny would obviously have to find out in order to help her and/or not to act insensitive and step on a landmine...