A child born to non-Jews is understood halakhically to be not related to his father. To the extent that identical twins are not considered related. Plus, the story of Niftayim the convert, who didn't have to be concerned about the illicit sexual familial relations. Among several proofs that make the same point. Plus, 2 statements by R. Akiva, including one point about converts and one about Jonah the prophet. Also, a mishnah of the mixed up cases of which child belongs to whom. What are the implications for yibum?