וְגַם־אָמְנָ֗ה אֲחֹתִ֤י בַת־אָבִי֙ הִ֔וא אַ֖ךְ לֹ֣א בַת־אִמִּ֑י וַתְּהִי־לִ֖י לְאִשָּֽׁה׃
And moreover she is indeed my sister, the daughter of my father, but not the daughter of my mother; and so she became my wife.
Read kabbalistic (mystical) interpretation of Genesis 20:12: and classical mystical sources.