Is this irony, in "My Last Duchess"?

Hi All,

I am trying to figure out if these two lines in Robert Browning's monologue, "My Last Duchess" would be considered irony.

"“That’s my last Duchess painted on the wall, Looking as if she were alive.”

I am having a very, very hard time finding the irony in this piece because poetry/monologues/literary art is not my strong point and I have to write an essay on it... My professor's notes on my revision say that what I'm lacking is leading the reader to an appreciation of the aesthetics of the work of art and in the textbook... his interpretation of doing this is by pointing out the irony in this piece... So any and all help would be greatly appreciated.

This for a college English 2 literature class paper.

Thanks so much