"Eddin: Anything new to report about Bergen? Brant: None, my lord. His boy, Jacke, turned himself in and pleaded mercy. He is currently in the dungeons. Eddin: I suspect he has retreated to the Iron Islands. As long as he isn't in the Borderlands any longer, he has been stripped of his power. Leave Edgarth. We now face a bigger threat."
After discovering his true allegiance, he has been attainted by Eddin Blackgard and branded an outlaw. After this, he and his servant Grandon as retreated to the Iron Islands while his castle, the Iredale Fort, has been taken by the Blackgards.
After his spectacular defeat during the Assault of Blackgard, Edgarth was captured and later executed for treason. After the battle, Eddin Blackgard allowed Edgarth's son, Jacke Bergen to keep the Iredale Fort, but the Bergens lost their lordship and nine-tenths of their lands was distributed among neighbours who were more fervent in their support of Eddin. House Bergen's status thus fell from from being a full noble house to a knightly one.
Edgarth was transported to Blackgard where he was tried for treason and for atrocities against civilians in war. "sparing neither age nor sex, septon nor septa." He was crowned with a garland of oak to suggest he was the king of outlaws. He responded to the treason charge, "I could not be a traitor to Eddin, for I was never his subject."
Following his trial, Edgarth was taken from the hall to the city dungeons, then stripped naked and dragged through the city at the heels of a horse to the public executions square. He was hanged, drawn and quartered — strangled by hanging, but released while he was still alive, emasculated, eviscerated and his bowels burned before him, beheaded, then cut into four parts. His preserved head (dipped in tar) was placed on a pike atop the gates of Blackgard. His limbs were displayed, separately, in the Iredale Fort, Sandkeep, the Cragmire, and Oakwell.
Spoken by Edgarth
"Grandon, I have heard that you succeeded in poisoning Grayson Mercer. Soon you will need to leave your post at Dunharrow. News of Grayson's death will soon reach Blackgard and it won't take long to find out that I'm behind everything. I've been communicating with Marlen and informed him that he needs to start abusing his wife again to lure Dyron away from Blackgard. I'm coordinating with some of the Blackwatch right now to have Dyron eliminated once and for all. With Dyron out of the way and Trevyr becoming too sick to rule the Borderlands, laying siege to the Black City will be simple. Thank goodness I don't need to pretend to be Glendon Estermont's ally anymore or worry about finishing them off, as Victarion Greyjoy now controls Storm's End since they left to rejoin Stannis up North. Now all that needs to be done is to tell King Balon to start the attack. I'll be waiting for you at the Iredale Fort. Report to me there. Yours endearingly, Edgarth Bergen, Lord Defender of the Borderlands."
―Edgarth's instructions to Grandon that were discovered by Maester Caledon.
"Euron Greyjoy: You're Bergen, right? That lord from the Borderlands that my brother was conspiring with? I did not expect you to be here. Edgarth: I had to. The boy now knows. That fucking coward Rosby betrayed us. I told Balon that he couldn't be trusted! Euron Greyjoy: Well, if he's a craven now, then he's always been a craven, and we are better off without him. Edgarth: What do we do now, your Grace? Euron Greyjoy: We now have the ships, the soldiers, the gold. We are ready. I guess this is the one thing Balon did right. (laughs) Edgarth: Let me accompany you, my king. Euron Greyjoy: No. Edgarth: What?! Why?! Your brother and I had been planning this long before you were ever in the picture! He promised me Blackgard! He promised me that I would rule the Borderlands! He promised me Eddin Blackgard's head on a spike! Euron Greyjoy: Patience, Bergen. You should hold that tongue, unless you want to lose it. Edgarth: Forgive me, your Grace. Euron Greyjoy: And do not worry. I will give you everything my brother promised you and more."