‘In waiting’ When does the title change hands?
Marrying an heir to a Dukedom does not mean you will become a Duchess as soon as the generation above you passes away.
According to Debrett’s, between the death of a Duke and his funeral the incumbent Duke and Duchess are officially “in waiting”.
The new Duke and Duchess are then styled as such after the funeral, at which point the Duke’s widow becomes the Dowager Duchess. While the Duke and Duchess are married, the Duchess also holds the title of “chatelaine” – a French term which refers to her being the mistress of the house.
If the couple were to divorce, the Duchess’s name would subtly change. For example, while married to the Duke of York Sarah Ferguson was referred to as “the Duchess of York” but after their divorce, she became Sarah, Duchess of York.
Any new wife of the Duke would then take on the title “Duchess”.