Is it permissible for the father of the husband to see his son's divorced wife, who is now married to another man, after she was irrevocably divorced from his son by three pronouncements, without hijab?

As soon as the marriage contract is concluded with a woman, she becomes unlawful for the husband's father, based on the Almighty's saying: "and the wives of your sons who are from your own loins." This prohibition is perpetual, and the father is permitted to look at her as he would look at his unmarriageable kin (mahram).