How do I tell my daughter about her dad

How do I tell my 12 yr. old, that her father (stepfather) who has raised her since she was three months old is not her biological father? Her father (stepfather) and I are still together and have 2 other children. Her bio dad has recently got out of jail after 7 yrs and now wants a blood test, before he gives up his parental rights.  So, back to my question how should I tell her and how much should I tell her about her bio dad?

[Kevin Kennedy, Ph.D.]

The best approach is a simple, clear, straightforward one. Tell her the truth, including how you and her father came to be together, what occurred to explain his absence from her life, icluding his incarceration. Then be available to respond to her questions, concerns. So the rule of thumb, so to speak, is to be truthful in as asimple and clear way as possible.