What is the ruling on a man marrying his nephew's wife after his (the nephew's) death or divorce?

It is permissible for a man to marry his brother's son's wife, or any other relative's wife, after her divorce or his death and the expiry of her 'iddah (waiting period). Those women who are forbidden (for marriage) are the wives of fathers and grandfathers, and the wives of biological sons, for Allah, the Almighty, says: "And do not marry those [women] whom your fathers married" (Quran 4:22), and His saying: "and the wives of your sons who are from your [own] loins" (Quran 4:23).