In Book 3 Loreon Casterly ends up killing his father and cousin, Tywon and Jayna, he attempts to kill himself after but his attempt fails. Taena Skies has him set sail towards Rhaenerys Blackfyre, who at the time was at Dragonstone but was preparing to leave to King's Landing, meanwhile Jamie Casterly is unaware that his brother is with Rhaenerys. Jamie vows vengeance against Loreon but he is now the new lord of Knife's Edge and The Proudlands, and with Rhaenerys the new queen Jamie must swear allegiance towards Rhae. Jamie has never been supportive of Aeyron Archer but will he bow to Rhae after seeing Loreon by her side? Will the Kingslayer become the Queenslayer too?
There is the possibility that Jamie does not swear fealty towards Rhaenerys and instead Jamie becomes disinherited by Rhae and Loreon becomes the new lord of the Proudlands. Tywon Casterly must be rolling in his grave at that thought and it would be dramatically ironic if it did come true. Tywon had a firm hand on his kingdom but now with him dead and two incompetent politicians, in Loreon and Jamie, can either of them hold their kingdom together? It seems that Jamie may have his hands full with his kingdom to go after Loreon, or perhaps he decides to leave his father's legacy behind and attempt to bring Loreon to justice.
How can say what happens to Loreon too? Taena must have had a plan with Loreon by sending him to Rhae but with Taena died what happens now? Does Loreon even live, will Rhaenerys even allow a kinslayer in her own ranks? There also is the question of the marriage between Jamie-Rhaenerys, Loreon-Saerenna, but now with Tywon died will that marriage even happen? Loreon does have the parchment containing the marriage offer but he admits to his father that he could not convince Nymeria(a princess) to marriage, so how will he convince Rhaenerys the Queen to marriage?
The future does not look positive for House Casterly - Tywon's death will devastate the kingdom of The Proudlands. Loreon Casterly did not know what he set off when he set the crossbow in his father's chest, neither him or Jamie Casterly could dear hold the kingdom. All of Tywon's plans seem to crumble too as the marriage may not happen anymore, if Jamie continues vengeance against Loreon he may end up dead and a suicidal Loreon will be left as Lord of The Proudlands...