All,

I want to know how to prove whether someone is a half-sibling or cousin.

My results from Ancestry.com show us a match as First cousins. We both have different mothers, she knew her father, but he passed away in 2001, and I never knew who my paternal side of my family was until I submitted DNA and got results here.

All indications point to her being my half-sister and him being my father (including a striking resemblance).

However, we really HAVE to know conclusively that we are half-siblings. Her father (and likely my father) had one brother and a few sisters.

We show up as ~25% shared DNA on here and another major DNA testing site.

With her father having passed away in 2001, how can we prove this absolutely conclusively?

I also had my mother's DNA sent in for testing and she shows as my mother, and I can then sort out Paternal vs. Maternal DNA.

If I have the RAW data for both my half-sister's DNA test and mine, is there a way to absolutely conclusively prove we are half-siblings?