My mother own father, sister and I?

I need to figure something out. Of my mother was sexually assaulted by her own father, and then sad a son which is me, but had my sister by by a different guy that was not mother father. Do that make me and me sister blood or step siblings? Need opinion. Why does it matter because to me it does. So if someone can take this seriously and help me figure this out that would be great.
My mother own father, sister and I?
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