Deuteronomy 22:30

A man shall not take his father's wife
Not marry her, whether his own mother, or a stepmother; or even, as Aben Ezra thinks, anyone that was deflowered by his father. Jarchi interprets it of his father's brother's wife, which he was obliged to marry by virtue of the law in ( Deuteronomy 25:5 )

nor discover his father's skirt;
or lie with her his father had thrown his skirt over, or married; and which being the first, is mentioned here as a sample to all the rest forbidden ( Leviticus 18:7 ) or, as Bishop Patrick expresses it, is a "short memorandum", to make them careful to observe all the other laws respecting incestuous marriages and copulations there delivered.