Wait, they are talking about the countess being related to the royal family, but she's a princess of a neighboring country? So I guess either the Queen of the next country is related to the King of this country. (assuming a patriarchy which this series has been described as so far). If so then it's pretty surprising that the Duke wasn't engaged to the Countess if only to ensure the political standing between the two countries. A Duke is generally a blood relative to the King and connecting him to the countess, who is a princess of the neighboring kingdom and also blood related to the royal line makes more sense than engaging him to some random noble lady. Especially since they already had a relationship. That is unless Mrs. Mason is much older than him (yes, I know Mrs. implies she is already married, I'm talking about in the past).