Is it permissible for the wife not to wear hijab in front of the father of her husband's mother (the husband's maternal grandfather)?

The husband's maternal grandfather is considered a mahram to the wife, and she is permitted to display her adornment before him, without extravagance, based on the Almighty's saying: "And not display their adornment except to their husbands, or their fathers, or their husbands' fathers." For the daughter's child is considered a child of their mother's father, just as Jesus, peace be upon him, was counted among the progeny of Abraham, peace be upon him, through his mother Mary.