My (38M) daughter (13F) isn’t biologically mine. How do my wife (35F) and I finally tell her?

Hello.

I started dating my wife when she was 4 months pregnant with her ex's child. The ex was abusive and fled several states away when he realized she wasn't going to abort the baby.

I was there in the room when she gave birth, and daughter has always known me as her dad. We've been wanting to tell her the truth for a while but wanted to wait until she was old enough to process the information. But now it's getting to where I think it may be too late.

What is the best way to tell her? And what can I expect after the truth is revealed?