Marrying

[rebbonk]

Suppose you marry a widow who already has a grown up daughter and your father marries the widow's grown up daughter. Now the widow's daughter becomes your mother. Since your mother's mother is your wife, your wife is also your grandmother. As the husband of your grandmother, you become your own grandpa.

Spoiler:

Sweet home, Bed'uth.

[Melisandre]

and in Nuneaton.