Does a women have to wear Hijab in front of her husband's son? (husband is dead).

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The husband's son is a Mahram (unmarriageable man) to his father's wife. So, he can see from her that which could be seen by any other Mahram; i.e., the head and the extremities of the body (the neck, the feet, the arms…). Allah Says (what means): {… and not to reveal their adornment except to their husbands, their fathers, their husband's fathers, their sons, their husband's sons…} [Quran 24:31]

This ruling does not change by the death of the husband. But if this son is not religious and if he is perverse and there is fear of temptation, then the woman should veil herself and cover her head and extremities from him. We have heard of many aggressions from sons against their father's wives because of the leniency in this matter.

Allah knows best.