Erryk Cargyll
A knight of the Kingsguard, twin to Ser Arryk — he chose the queen, and carried Viserys's crown to Dragonstone in his saddlebags.
A soul born at Crackclaw Point, sworn to The Blacks — the Queen's Party, The Kingsguard.
The fuller tale
Season One
Rhaenys is locked in her chambers, courted for Meleys — and escapes with Ser Erryk through the crowds being herded to the Dragonpit. Ser Erryk Cargyll arrives with a stolen crown; Daemon sets Viserys's crown on Rhaenyra's head on the shore of Dragonstone.
Where they stand. King's Landing and Dragonstone.
Season Two
Ser Arryk Cargyll is sent to Dragonstone wearing his twin's face; Ser Erryk finds him at Rhaenyra's door. Twin kills twin in the black queen's hall — and Erryk, having slain his brother, falls on his own sword for the shame of it.
Their story
Arryk's twin serves the black faction, and when the crown splits between two royal households, Erryk chooses his queen over the king his brother still serves — a decision made easier, perhaps, by his physical proximity to Rhaenyra's household on Dragonstone at the moment the split occurs, but no less consequential for that.
His single most significant act before the duel that defines his ending is a quiet one: he carries Viserys's crown itself to Dragonstone in his own saddlebags, delivering to Rhaenyra the literal symbol of an inheritance the green council in King's Landing has just tried to steal from her.
When his own brother arrives at Dragonstone in disguise to kill the queen, Erryk is the one who recognizes the deception — a recognition that forces him into the single worst fight of his life, against the one person in the realm who knows him well enough that neither of them can hide anything from the other.
How it ends for them
On the screen. Fell on his sword for grief (S2·E2)
He carried Viserys's crown to Dragonstone and chose his queen over his king — and then killed the brother who chose otherwise. When it was done he wept, begged forgiveness, and fell on his own sword rather than live with the arithmetic.
On the page. Died of the same duel, weeping (F&B, ch. 3)
Twin met twin at Dragonstone's gates, white cloak against white cloak. The histories cannot even agree which brother struck the killing blows — only that both died of the meeting, and that the singers made it beautiful because no one could bear it plain.
In the show, Erryk kills the brother he recognizes beneath the disguise, and the grief of what he has just done overtakes him immediately afterward — he falls on his own sword rather than live with having killed his twin, even in defense of his queen.
Fire & Blood records the same double death but leaves the precise sequence of blows genuinely unclear — the histories cannot even agree which brother struck which wound first, only that both died of the same encounter, weeping, and that the singers afterward made the story beautiful because the plain truth of it was too painful for anyone to bear retelling straight.
Their chapters, book by book
Where the page and the screen part
The two tellings agree closely on Erryk's actions and their emotional cost; the differences are mainly in pacing and staging rather than substance, with Fire & Blood's account, as with Arryk's, offering more extended detail on the duel's length and anguish than the show's more compressed version allows.
Their journey
Where the two tellings send them to the same place the road runs whole; where they part, the screen keeps the left and the books the right.