There is a possibility he's not her biological father, & physically, I'm 99% sure she isn't his. I would never imagine ripping her life apart with that, because he has been a good dad, among with his family who absolutely adores her.

So first you lie and as if it wasn't bad enough to lie about child paternity you are also considering how to use this information at expense of ruining both your kid's and ex's life even posting about it online. I honestly don't understand how people are so shitty sometimes. But hey have an advice cause I will give you the benefit of the doubt that this post is of actual concern to your daughters well being and not about jealousy and self esteem issues you are going through. Don't ever try to use the fact that he is not the child's biological father, because it most definitely will backfire. He is the legal father now and as far as state is concerned he is the father responsible for that child. And if you for some reason try to distance your daughter from the father by giving your daughter this information I would dare say this is a good example of Child Psychological Abuse and the father can use this fact, and with all reason on his side, to get full custody as evidently you are not fit to be a mother. And don't get me wrong. You say

I would never imagine ripping her life apart with that

But if you really meant what you said you wouldn't even be posting this information in a legal advice post.