[House Martell — Houses]
It has long been believed in Westeros that only members of the Targaryen bloodline can easily bond with and ride dragons - which is one of the reasons they so readily accepted Daenerys (though that was also because she hatched them, becoming their adoptive mother). The revelation about Jon's real parentage means that he may potentially bond with one of Daenerys's three dragons in a future novel - after all, she has three dragons but only personally rides Drogon, the largest. To a lesser extent, this might also be true of the Baratheons - Robert was Rhaegar's second cousin in the books. With the deaths of Stannis and Shireen in the TV series, the only living member of the Baratheon bloodline is Robert's bastard son Gendry (who is, in fact, Jon's third cousin). House Martell also intermarried with the Targaryens but not recently, about a century ago: in the books Doran Martell 's middle son Quentyn (cut from the TV show) traveled to Meereen and explicitly hoped his small amount of Targaryen blood would be enough to make the dragons trust him and try to mount one, but he was instead burned alive by Rhaegal.
Cersei is annoyed at the Tyrells due to their nonstop demands, among them to wed Margaery to Tommen so soon after Joffrey's death. As time passes, Cersei's annoyance gradually turns into mistrust, and then to paranoia: she becomes convinced that the Tyrells, Margaery in particular, are plotting against her, have conspired with Tyrion to kill Joffrey and maybe her father too (she does not suspect Littlefinger at all). Her suspicions are fueled when a gold Highgarden coin is found in the cell of a jailer named Rugen (in fact, Varys in disguise), who disappeared the night Tyrion escaped; that makes her suspect the Tyrells - not Jaime - helped Tyrion escape by bribing the guards, and confirms her former suspicions about them. She has nightmares about Tyrion and thinks he is still hiding in the walls of the Red Keep, planning to kill her and her children. Until now, her obsessive hatred for Tyrion has effectively blinded her to the presence of her true enemies, believing that anything and everything that happens to her family was somehow Tyrion's doing (including the attempt of Gerold "Darkstar" Dayne to kill Myrcella – the end result of a plot instigated by a rogue member of House Martell who was actually trying to help Myrcella), and this obsession only grows after Tyrion kills Tywin.
Jaime is summoned by Cersei, who has received a "gift" from Dorne : an ornately carved viper, with Myrcella 's unique Lannister pendant suspended from its fangs. Both siblings understand the gift as a threat from House Martell . Even though she is equally to blame for covering up their incest, Cersei lashes out at Jaime for not being a father to any of their children, to which he points out that if he had been, their children would be stoned in the streets. Jaime declares that he will bring Myrcella home, but Cersei mockingly asks how a one-handed man can rescue a princess alone. Jaime tells her that he never said he was going alone.
Tyrion meets with Littlefinger and outlines a plan to wed Myrcella Baratheon to Robin Arryn to secure the support of the Vale . He promises to make Littlefinger the Lord of Harrenhal and Lord Paramount of the Trident in exchange for his assistance and swears him to secrecy. Pycelle is arrested for revealing that Tyrion plans to wed Myrcella into House Martell and Littlefinger realizes that he was involved in a ruse. He confronts Tyrion who apologizes and offers him another opportunity; to act as an envoy to Catelyn to propose a prisoner exchange.
In the second novel, while trying to broker an alliance for House Martell's support in the War of the Five Kings, Tyrion offers Doran Martell, among other concessions, to hand over Ser Gregor to face justice for the murders of Princess Elia and Prince Aegon. Tywin disapproves, claiming that Gregor has his uses, and every lord has need of a beast from time to time. Tyrion answers that "the woods are full of beasts", and Tywin says he'll think it over. Later, Tywin decides against the idea, stating that "Ser Gregor has served us well. No other knight in the realm inspires such terror in our enemies"; in order to appease the Martells, he comes up with the idea to put the entire blame on Amory Lorch (who is, quite conveniently, dead). As things turn to be, Tywin's new version of the death of Elia and her children does not stop Oberyn from fighting Gregor.