A stepmother is not a Mahram to her stepdaughter’s husband

Question 9: My father married a second woman and begot a son from her, can my husband be her Mahram (permanently unmarriageable relative) and see her without Hijaab (veil)? It is worth mentioning that my father is my husband’s maternal uncle and so she is the wife of my husband’s maternal uncle. Give us your Fatwaa’ (legal opinion issued by a qualified Muslim scholar) in this regard, may Allaah reward you with the best. 

Answer: The stepmother is not a Mahram for the husband of the stepdaughter. The Mahram relationship exists between the wife’s mother and the husband of her own daughter. Pointing out the female Mahrams, Allaah (Glorified and Exalted be He) says: …your wives’ mothers The stepmother is not a mother of the husband’s daughter of a previous wife… read more here.