What makes Robert Browning's Last Duchess a dramatic monologue?

Monologues are not dramatic all, but Robert Browning's My Last Duchess is a dramatic monologue because the fact of the Duke to have got his wife killed for looking and smiling at another person is revealed as if in a suspenseful drama only towards the end. Also the readers towards the end will jump in their seats to think whether the long line of the poet's previous wives would not have suffered the same fate. This poem is not a monologue in poetry but real drama condensed into poetry.