Arlan Dondarrion, third son of Thundering Triston Dondarrion, was born to the lord and his wife, Lady Cassana Dondarrion, in the year 350 AC. After he was conceived but before he was born, his father sheltered Baelon Targaryen’s family and personal guard from the wrath of the Jealous Dragon, King Aemon Targaryen. These events led to the War of the Shadow, which led in turn to Triston’s death. Lord Dondarrion believed that his family would be killed if Baelon’s side lost, so he sent his wife away to Braavos so that she and their unborn child would be safe from Aemon and the loyalists. After the war, his first son, Lomas, took up the title of Lord of Blackhaven. His second son, Harys, was sent to the Wall.
Lady Cassana and a company of Dondarrion soldiers traveled to Braavos, where her husband kept a manse. Disguised, they avoided Aemon’s efforts to find them and return them to Blackhaven. In 350 AC, Cassana gave birth to Arlan. The birth was difficult thanks to the stress she endured during the pregnancy, and she barely survived. While she grew to love her son over time, she resented him at first because his birth had almost killed her, and he was born broken. His left hand was deformed, with the last three fingers missing. The remaining digits were weak, and could be used for little of merit to a young nobleman.
Because of his surroundings and deformity, Arlan’s martial education was different from that of the average Westerosi lordling. The household guard tried to teach him the one-handed arming sword, but his left hand was so difficult to use that he could barely hold the shield he’d need to defend himself. Still, defending himself was a necessary skill. The master-at-arms hired a Braavosi water dancer in hopes that his instruction would at least give the boy a fighting chance in the streets of the city. The one-handed, sideface style was a perfect fit for Arlan. He became a well-known water dancer, to the point that many bravos would take a detour down a side street when they saw the young duelist coming. Few knew him to be a Dondarrion, though, as he took great pains to keep his presence covert.. Dying his hair and forsaking the typical Westerosi beard, he looked more like a bravo than a highborn. Arlan learned to be constantly on his guard, and he became an expert at spotting spies, even when they weren't looking for him.
On Arlan’s seventeenth birthday, his mother gave him a Braavosi sword, forged from fine steel and decorated with a purple stone in the hilt. He named it Sundowner, after the sea wind which blew out over Ragman’s harbor at sunset. While his swordsmanship won him the attention of several well-to-do Braavosi courtesans, he remained a bachelor for most of his life. His fancy was eventually captured by Alia, the daughter of a common fisherman. The two wed in the Braavosi custom in 376, and, to please Arlan’s mother, held a second ceremony in the manse’s small sept. The two had a son in 377, whom they named Beric after Arlan’s famous ancestor.
Arlan's espionage skills were bolstered by his occasional employment as an informant to the Iron Bank, which often sought information on the activities of other moneylenders in the city. Posing as a merchant, he would learn about how much the organizations were willing to lend for the purchase of ships and other useful goods, and report the prices to the Iron Bank.
While Arlan was far removed from his home at Blackhaven, he was not ignorant of the happenings there. He wrote often to Mandon, the maester of Blackhaven. Mandon was one of the few in Westeros who knew his true identity. This knowledge became important in the eleventh moon of 379 AC, when Lomas died in a riding accident. He left behind a single, sickly daughter. The other Marcher Lords, not knowing that Arlan still lived, believed that his cousin, Edric Dondarrion, was the next in line for the lordship, and promoted him as such. Mandon hurriedly wrote Arlan, who, upon hearing the news, went to stake his claim. He announced his return to Westeros with letters to the King, Lord Baratheon, and his fellow Marcher Lords. As of 380 AC, he has arrived at Blackhaven, where he lived for a few months before leaving for the Tourney atOldtown. There, he made it into the second round of the melee, and jousted in his first tourney.