It is here that one begins to realize that what he felt towards his wife was actually malice without a trace of love.
Moreover it becomes clear that he tells this marriage broker about the faults of his last wife specifically to advise what he will and will not tolerate with the next wife. While he does not state with specificity how his new wife is to conduct herself, it is clear that she will only exist as a result of his mercy. Indeed, the new wife is already set up in a trap because she will be demanded to figure out what her role is as his duchess which is impossible.
This situation could be compared to women of royalty, first ladies, and wives of powerful men. Women whom are the wives of powerful men are expected to enhance their husbands. They are not supposed to find joy or amusement in anything other than that which their husband does and they are aware that they are a direct reflection of the man they are married to. In My Last Duchess, it is clear that the Duke is appalled that the deceased duchess did not hold her name and position in society to its' proper level. Indeed, as far as the Duke is concerned, it is his name and position that should have been paramount to everything -- his "gift of a nine-hundred-years- old name.".