Edmyn was the first riverlord to raise his banners in support of Aegon. His troops marched with Aegon's to the newly constructed castle of Harrenhal, where the lineage of House Hoare is ended by the dragon fire of Balerion. After the defeat of Harren, Edmyn was granted dominion over The Riverlands and styled Lord Paramount of the Trident. He was possibly chosen for this job because other possibilities, such as House Bracken or House Blackwood, were less politically stable.
One of Edmyn's daughter was married to Quenton Qoherys, the new Lord of Harrenhal. Edmyn would go on to serve as King's Hand for Aegon during the years 7-9.