They're husband and wife? They look exactly alike, hair color, eye color, everything. I ...

If you look very closely. The shade of blue is different. The duke has a deeper slightly purple tone to his eyes, and the wife had a lighter sky blue with no other accent.

She is the princess and the royal line is blond
And the ducal house was stated as also related to the royals
They're like very very distant cousins

Now that i looked at it. True

Thanks ヾ(☆▽☆)