Myrcella Baratheon
The princess of the realm, sweet-natured and biddable, the middle of Cersei's three children.
A soul of House Lannister, born at King's Landing.
The fuller tale
Season One
The younger, quieter version of her family — closer to Sansa than to either of her brothers, and the one Baratheon child who seems to notice when the people around her are unhappy. She watches her father's court from its edges for most of the season, and by the end of it Tyrion has traded her away to Dorne as a bride for Prince Trystane Martell, a piece moved to secure an alliance rather than a happiness. She leaves King's Landing without much say in the matter, young enough that no one thinks to ask her opinion of it.
Season Five
Grown now, genuinely fond of Trystane rather than merely assigned to him, and settled enough in Dorne that when Jaime arrives in secret to bring her home she does not particularly want to go. Ellaria's grief over Oberyn very nearly gets her killed by the Sand Snakes before Prince Doran steps in to stop it, and on the boat back to King's Landing Jaime finally tells her the truth about her parentage — that he is her father, not her uncle — and she tells him she already knew, and that it changes nothing about how she feels about him. Ellaria's goodbye kiss on the dock turns out to have been the real weapon all along: Myrcella bleeds from the nose crossing the water and dies in Jaime's arms within sight of home.
How it ends for them
On the screen. Poisoned in Dorne (S5·E10)
Ellaria Sand kissed the princess farewell at Sunspear's docks with poison on her lips. Myrcella died at sea in her father's arms — moments after telling Jaime she knew, and was glad.
In the show she dies of a kiss. Ellaria Sand, unappeased by peace with the Lannisters, bids the princess farewell at Sunspear's docks with poison on her lips — the long farewell, an antidote taken by the poisoner alone — and Myrcella sails for home apparently well. The venom works on the water: moments after telling Jaime she knows he is her father and is glad of it, she bleeds from the nose and dies in his arms, the second golden shroud of Maggy's prophecy delivered mid-embrace. Ellaria's price is paid later, when Cersei returns the exact kiss to her daughter Tyene in the black cells. In the published books Myrcella is alive — scarred by Darkstar's blade during the collapse of Arianne's plot, short an ear, but breathing, and on her way back into the story's center as Dorne weighs its next move.
Their chapters, book by book
A Clash of Kings 2 chapters that name them
A Feast for Crows 2 chapters that name them
Where the page and the screen part
The books send her to Dorne on the same logic and into a much more tangled story. There she becomes the centerpiece of Arianne Martell's queenmaking plot — a Dornish scheme to crown Myrcella under Dornish law, which recognizes the eldest child regardless of sex — and when the plot unravels, the knight called Darkstar turns his blade on the child herself; book Myrcella survives him, but maimed, losing an ear and carrying the scar across her cheek. None of it — Arianne, the queenmaking, Darkstar — reaches the show, whose slimmed-down Dorne plot substitutes the Sand Snakes' vengeance for the books' constitutional crisis. She also gets a different confidence: the books have not given her the paternity scene with Jaime, which is the show's own invention and arguably its best addition to her.
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.