Game Of Thrones: 10 Storylines From The Books The Show Ignored
4. A Dance With Dragons Part III - Aegon Targaryen
The third character travelling the eastern world to meet Daenerys is in secret a dragon himself. Everyone knows the Mountain killed Elia of Dorne and her two children, however in the books Varys and his friends across the Narrow Sea conspired to save the life of the little boy, swapping him without anyone knowing and sending him into exile.
Posing as Young Griff, Rheagar's son Aegon, and his "father" Griff (actually former hand of the king Jon Connington) originally planned to reveal the dragon's true identity to Daenerys, join forces with her and storm Westeros together. This changes when Tyrion Lannister convinces the young boy that he doesn't need Daenerys to take Westeros. Instead he should head home himself and let Dany come to him.
Young Griff takes this advice, and with the Golden Company at his back, invades Westeros, takes Griffin's Roost and sets his sights to Storm's End. By the end of A Dance With Dragons, Kevan Lannister is aware of Aegon's presence and threat. In Cersei's absence he has taken big steps in calming the storm between Lannister and Tyrell, when Varys appears for the first time since Tywin's death, killing Kevan with a crossbow.
This is a calculated move from the Spider to undo all the good work Kevan has been doing, throwing the crown back into turmoil, making Westeros all the easier for Aegon to take.