House Brightstone

House Brightstone was founded by three brothers, Albion, Ragnar, and Royland Brightstone, in the Vale. Together, they formed a powerful triumvirate that balanced out each other's weaknesses and made House Brightstone much greater than the sum of its parts. The brothers were skilled warriors and cunning strategists, and they quickly conquered the Vale, defeating House Egen and House Baelish with ease. 
With the Vale under their control, House Brightstone set its sights on Kings Landing. They sailed to Gulltown and with the help of House Lannister, they were able to defeat the Targaryens with relatively little resistance. The Triumvirate was named kings of the Andals, the Rhoynar, and the First Men, and House Brightstone became one of the most powerful houses in Westeros.
As they moved into the Riverlands, House Arryn rebelled against them with help from House Mallister and House Stark. The majority of the fighting took place around the Riverlands, with Mallister and Arryn's decision to attack by land causing some problems for House Brightstone. However, ultimately, House Brightstone emerged victorious from this conflict as well.
After the Riverlands war, House Brightstone faced several other rebellions. These included the Targaryen Revolution, the Saga of Two Kingdoms, and the Daynish War. Each time, House Brightstone was able to defeat its enemies and maintain its hold on power.
However, after the Daynish War, House Brightstone disappeared without a trace, leaving the realm with no one to lead it. The exact reason for the disappearance of the Triumvirate is unknown, but some speculate that they may have been killed by a rival house or that they may have simply decided to retire from politics and live out their days in peace. Regardless of the cause, the disappearance of House Brightstone led to the demise of the realm as a whole, as other houses vied for power and eventually tore the kingdom apart.