This is where he encountered Prince Doran Martell (Alexander Siddig), and many fans speculated that Doran’s eldest child, Arianne, would be involved, after playing a major role in the books.
Instead, her sibling in the book, Trystane (Toby Sebastian), was involved, but this didn’t stop book readers from being disappointed by the absence of Arianne.
Her role was of major significance in the books as she ended up plotting for Myrcella Baratheon to take the crown of the Seven Kingdoms, she is also set to continue her role in the Winds of Winter.
Her role in the series could have meant an entirely different fate for the Targaryens.
source: express.co.uk