In Act I Scene 4 of Macbeth, what is an example of dramatic irony?

Let us remember that dramatic irony is defined as one
character or several characters and the audience possessing knowledge that another
character or group of characters does not have. What is key to note in this scene is
that it is juxtaposed or placed next to Act I scene 3, which is when Macbeth receives
the prophecy from the witches that has such a big impact on his life. In this prior
scene, Macbeth shows himself to be seriously considering how he might become King as the
prophecy suggests. It is then highly ironic that he plays the role of loyal subject and
that Duncan is so naively trustful of him. Note the intense irony when Duncan comments
about the previous Thane of Cawdor who has just been
executed:

readability="7">

There's no art

To
find the mind's construction in the face:

He was a
gentleman on whom I built

An absolute
trust--

However, having
realised this valuable life lesson, Duncan goes on to repeat exactly the same mistake.
He does not have the "art" to see what is going on in Macbeth's mind and is taken in by
the act of his loyalty, once again building an "absolute trust" in someone only to be
betrayed, and this time killed, by them. Thus, the dramatic irony serves to emphasise
the good nature of Duncan and his naive character. He has not learnt his lesson from the
treachery of the former Thane of Cawdor and is once again too quick to trust too
quickly, with devastating circumstances.