The story ends with the duke and the agent leaving the gallery to meet the Count below.
Throughout the story, the duke is obsessed with obtaining the sole special attention of his wife, who unknowingly foiled this by experiencing delight in everything around her. The duke never bothered to have a real relationship with his wife, he would rather control her in any way he can. The duke relishes his prestige and believes that his wife should only take delight in his presence. His overbearing arrogance led him to the conclusion that everything should be centered on him, especially his own wife. Unfortunately, his wife did not understand this belief and continued to enjoy life whenever she can. The duke's jealousy and insecurities would not allow him to be denied of his spotlight, and so he gave orders to dispose of his wife. .
He describes these events to the Count's agent in order to deliver a message detailing the expectations of his next duchess. The duke of Ferrara is indeed a powerful man to have his wife murdered and tell about it in order to negotiate for a more "proper" wife. This great power that was undeservingly bestowed upon the duke by the name of Ferrara is what twisted him into the arrogant murderer that he has become. Power will inevitably spawn the greed for more power. The power that the duke seeks in the story is the sole power over his last wife. Since he could never attain power over her in life, he holds it in death, in the form of her portrait. Now her smile is indeed his: "but to myself they turned" (line 9). The duke keeps the portrait covered because he is like a jealous and emotionally insecure child; he wants to show complete possession of the Duchess's smile.
The next point revolves around the duke's passion for art. The passion can be indulged with wealth and prestige. The duke realized that he could never hold the special interest of his wife, and so he had her transformed into art.