What is the central irony used to support the satire in the passage?

What is the central irony used to support the satire in the passage? The king prefers a pretentious son to his more sensible siblings. The king finds great value in a son who has little sense. The king is unable to see that Shadwell is really a poor choice. The king believes that maturity will build more sense in his son. Done Mac Flecknoe by John Dryden (excerpt) All humane things are subiect to decay, And when Fate Summons, Monarch's must obey; This Flecknoe found, who like Augustus young, Was call'd to Empire, and had Govern'd long; In Prose and Ver