The husband's grandfather as a Mahram

Q: I am a woman who is married to a person who is not one of my relatives. Is it permissible for me to expose my face in the presence of his maternal grandfather? I think that I am Mahram to him (unmarriageable relative to him) but my husband objects to this. Could you kindly advise? (Part No. 17; Page No. 355)

A: A husband's grandfather whether maternal or paternal is a Mahram to the wife of his son's son or the wife of his daughter's son. Allah (Exalted be He) says concerning Mahrams: ...or their husband’s fathers The grandfather is considered to be a father from any side. Allah knows best. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.