A Storm of Swords
Following the Battle of the Blackwater, during which House Florent fought for Stannis Baratheon, Brightwater Keep and all of its lands and incomes are granted to Lord Mace Tyrell's second son, Ser Garlan Tyrell, thus establishing House Tyrell of Brightwater Keep. Brightwater's former lord, Alester Florent, is imprisoned by Stannis at Dragonstone for seeking peace with House Lannister.
A Feast for Crows
From King's Landing, Garlan brings half of the Tyrell strength back to the Reach to press his claim on Brightwater, which is held by its castellan, Ser Colin Florent. When news comes of the fall of the Shield Islands, Garlan begins to gather men from across the Reach to retake the islands from the ironborn.
A Dance with Dragons
Davos Seaworth recalls that when Stannis decided to aid the Night's Watch at the Wall, Melisandre burned alive Alester Florent, the former Lord of Brightwater Keep, in order to obtain favorable winds for their expedition to Eastwatch.