How is Browning's poem "My Last Duchess" a dramatic monologue

First published in the collection Dramatic Lyrics in 1842, "My Last Duchess" is an excellent example of Browning's use of dramatic monologue. Browning's psychological portrait of a powerful Renaissance aristocrat is presented to the reader as if he or she were simply "eavesdropping" on a slice of casual conversation. As the poem unfolds, the reader learns the speaker of the poem, Duke Ferrara, is talking to a representative of his fiancée's family. Standing in front of a portrait of the Duke's last wife, now dead, the Duke talks about the woman's failings and imperfections. The irony of the poem surfaces as the reader discovers that the young woman's "faults" were qualities like compassion, modesty, humility, delight in simple pleasures, and courtesy to those who served her.