The Torah commands in Parashat Ahareh-Mot (Vayikra 18:15), “Ervat Kalatecha Lo Tegaleh” – it is forbidden to have intimate relations with one’s daughter-in-law, the wife of his son. This prohibition applies even if the son only betrothed a woman, without completing the marriage; once the betrothal occurred, the father may not have relations with the woman. Furthermore, even after the son dies or divorces, his father may not marry the son’s wife. She remains forbidden for the father for all time. This prohibition applies even if the son is a Mamzer – the product of an adulterous or incestuous relationship. A Mamzer is recognized by Halacha as his biological father’s son, and thus a Mamzer’s father is forbidden from having relations with the Mamzer’s wife. The Rabbis extended this prohibition to include the wife of one’s son’s son, or the wife of his son’s son’s son, for all generations. They further enacted that one may not marry the wife of one’s daughter’s son. This prohibition, however, does not extend further than the first generation; one may not marry his daughter’s daughter-in-law, but that daughter-in-law’s daughter-in-law is permissible. This prohibition against having relations with one’s daughter-in-law applies in all times and in all places. If one engaged in such a relationship in the presence of two witnesses who warned him in advance, then he is liable to Sekila (execution by stoning). If a person transgressed without witnesses, then he is liable to Karet. For an unintentional violation of this command, one must bring a Hatat (sin-offering). If someone had relations with one of the relatives with whom intercourse is forbidden by force of Rabbinic enactment – such as with his grandson’s wife – then he is liable to Malkut, as ordained by the Sages.