From: Rabbi Moshe Sofer
To: Rabbi Meir
A man known for nearly thirty years as Eliyah's biological son married Eliyah's sister, creating a potential Torah-level prohibition of marrying one's paternal aunt. The Chasam Sofer rules the marriage is forbidden based on the long-standing chazakah of paternity, which cannot be overturned by the father's belated denial, amatlah, yakir, or witness testimony. The woman requires a get from Avraham and is subsequently forbidden to a Kohen.
Source: Shu"t Chasam Sofer EH I §76