I had my DNA tested through Ancestry. About a year ago, my great nephew (I'll call him GN-1) whom I raised had his tested. The match came up Close Family–1st Cousin Shared DNA: 1,576 cM across 69 segments. His mother is my sister's child, my niece. My sister always claimed she didn't know who the father was.
We didn't think much about it till another great nephew (2nd sister's child) tested. He tested 1st–2nd Cousin Shared DNA: 706 cM across 30 segments.
Why is my great nephew (GN-1) testing so much closer to me?
He should fall in the range of the GN-2- under 850.
My sister told me once that our own brother raped her, but denied he was the father of her child (my niece, GN-1's mother).
Is it possible that my brother fathered my sister's child and that he is actually the grandfather of GN-1??
Could that be why our DNA is match is so high?
Could my niece be my sister?