Context:
Poem structure and historical backgroundThe poem is written in 28 rhymed couplets of iambic pentameter.
The poem is preceded by the word Ferrara:, indicating that the speaker is most likely Alfonso
II d'Este, the fifth Duke of Ferrara (1533–1598) who, at the age of 25, married Lucrezia di Cosimo de' Medici, 14-year-old daughter of Cosimo I de' Medici, Grand Duke of Tuscany, and Eleonora di Toledo.
More:
http://en.wikipedia.org/wiki/My_Last_Duchess