How does Browning's use of form evoke ideas of power and control in 'My Last Duchess'?

Publicly labelling his 1842 poem 'My Last Duchess' a 'dramatic lyric', Robert Browning clearly demonstrated a certain formal preoccupation with his work. His dramatic monologue is formed from one long stanza and attempts to denote a conversation between the Duke of Ferrara and the envoy of his future wife's father. However, the ‘conversation’ remains a one-sided monologue whereby the Duke depicts the nature of his last duchess and her tragic fate. Here, Browning manipulates the poem's form to demonstrate both the Duke's power and control whilst simultaneously undermining it. Arguably the long, single stanza presents the Duke as effortlessly powerful: his ability to captivate an audience and silence his guest (just as he silenced his late wife) is suggestive of an inherent power and authority that matches his noble position. Furthermore, he uses of Iambic Pentameter which, while verse, gives the impression of prose or everyday speech. Suggestive of ease and confidence, the prose-like sound of the poem portrays the Duke as calm, very much within his element. Yet the complex verse beneath such words belies a cunning, manipulative hidden character and thus the Duke appears to reveal far more about himself than he does the Duchess. In this sense, Browning's structure also serves to undermine the Duke's assumed power. This sense of uncontrollable revelation can be demonstrated both in the long, rambling stanza (suggestive of a lack of elegance and control) and also in the consistent use of enjambement throughout: ‘there she stands | as if alive.’ With words spilling from line to line, the Duke fails to control his words. Even the prose-like sounding verse may, arguably, demonstrate an lack of power to elevate his style to a more authoritative or lyrical sounding verse. Such lack of control or command over his words therefore serves to demonstrate a disparity between the power he perceives himself as possessing and the power he actually has. In this sense, Browning uses form just as he uses other poetic devices in ‘My Last Duchess’: to endow the Duke with a superficial sense of power and to then subtly undermine it.