King Henry the Fifth “was not angry since (he) came to France // Until th(e) instant” (IV.vii.54-55) he discovers that the boy has been killed by the French. The king’s been insulted, has faced military losses, and has had to allow a childhood friend to be hanged, but only NOW is he angry. Why? What is it in the character of the boy that elicits such a response?
When we first meet the boy in this play (we saw him three times in The Second Part of Henry the Fourth), he is in the tavern, calling forth the trio of Bardolph, Nym and Pistol to come to his “master” (II.i.79) Falstaff, as he dies. But his importuning comes with an insult “Good Bardolph, put thy face between his sheets, and do the office of a warming-pan” (II.i.81-82). This is reminiscent to our early observations of Hal in the tavern life back in The First Part of Henry the Fourth: “Thou art so fat-witted, with drinking of old sack” (1HIV, I.ii.2). The boy, hired by Hal to be the old knight’s page, is very similar to the boy prince.
Later, when the soldiers get to France, the boy wishes he was back in the tavern: “Would I were in an alehouse in London! I would give all my fame for a pot of ale and safety” (III.ii.11-12). This wish for drink sounds very much like Hal’s first appearance in The Second Part, when the prince tells Poins that he “desire(s) small beer” (2HIV, II.ii.6).
In the very same scene, once the men have been forced back to the front, the boy reveals to us what he thinks of his tavern-mates:
As young as I am, I have observed these three swashers. I am boy to them all three: but all they three, though they would serve me, could not be man to me... They will steal any thing... They would have me as familiar with men's pockets as their gloves or their handkerchers... I must leave them, and seek some better service
— III.ii.27-29, 40, 46-47, 50
He’s a young man who realizes his companions are not fit; in this, he sounds like young Prince Hal, who in The First Part tells us that he “will awhile uphold // The unyoked humor of (the tavern’s) idleness” (1HIV, I.ii.188-189). He’s played with them, but knows he must leave.
The boy understands and speaks French (as he translates for Pistol to the older man’s prisoner of war); Henry, too, “entendre (French) better que” (V.ii.264) than some French themselves do. And this deeper knowledge is a double-edged sword: insight brings a foreboding knowledge of what will come:
the French might have a good prey of us, if he knew of it; for there is none to guard (the luggage) but boys
— IV.74-76
He can see, sadly, what will come; so did Hal, as he foresaw that he himself would not “hang a thief…(but Bardolph) shalt” (1HIV, I.ii.61-62). In both cases, the prediction comes to pass, with deadly results. Bardolph steals a cross and must be hanged, and the French do attack the luggage and the boy is killed.
And we are full-circle with the now suddenly angry Henry.
Why is he so angry?
Because he sees his last link to his childhood happy times cut. He sees, in the death of the boy, the death of his own childhood.