Charles Ellicott Commentary Leviticus 18:12

"Thou shalt not uncover the nakedness of thy father`s sister: she is thy father`s near kinswoman." — Leviticus 18:12 (ASV)

Your father’s sister. —According to the law that was in effect in the time of Christ, this prohibition not only extended to the father’s half-sisters, but even when they were fathered by the grandfather illegitimately. It is remarkable that Moses himself was the offspring of such an alliance, since his father Amram married his own aunt Jochebed, who was his father's sister. (See Exodus 6:20.)