Comment by Rahaf on Baby Snow Leopard of the Black Leopard Family - Chapter 32

@Rahaf
I think the Grandpa is the Duke currently. Once he passes his title on through abdicating or death, the Marquis will take the title.
It's actually a historical accuracy, which is pretty cool.
"The son and heir apparent of a duke may use one of his father's lesser peerage titles by courtesy, which is often a marquess (marquis) if the duke holds such a subsidiary title."