The Battle of the Redgrass Field was the battle that ended the Blackfyre Rebellion and confirmed Daeron II's rule over the Seven Kingdoms.
Daemon Blackfyre and both of his eldest twin sons were slain in the battle by Lord Bloodraven (the Kinslayer) with apparently magical arrows. Ser Duncan the Tall's old master fought in the battle and lost his original squire in it, as did Ser Eustace Osgrey, who later appears in The Adventures of Dunk and Egg, as well as both of his sons. Ser Eustace fought for Blackfyre and for his treason lost all most all of his lands, his dignity, daughter and wealth.