Their parentage is disputed. Addam and Alyn's mother Marilda of Hull claimed they were fathered by Corlys' son Ser Laenor Velaryon. However Laenor is thought to have been gay, making this story dubious. It is widely believed Corlys fathered the boys, but did not wish to offend his wife, Rhaenys.
The Dragonriders, including Addam, attacked King's Landing, which soon fell to them, though Rhaenyra's half-brother Aegon II disappeared. Addam remained in the city to defend it, at the Dragonpit. However at the Battle of Tumbleton two other dragonseeds, Hugh Hammer and Ulf the White (also known as Ulf the Sot), known as the Two Betrayers, joined the Greens, meaning the Blacks lost the battle. The loyalty of the dragonseeds was questioned, Corlys was the only member of the Black Council who supported Addam. Rhaenyra ordered the arrest of Addam, however he was forewarned and fled the Dragonpit on Seasmoke. For warning Addam, his "grandfather" was beaten and imprisoned.
However Addam remained loyal to Rhaenyra and wanted to prove not all bastards were treacherous. He gathered an army of almost 4000 for the Second Battle of Tumbleton, and attacked the Greens at night. In the battle Hugh was slain by the Greens for planning to usurp the Iron Throne himself, and Prince Daeron the Daring, Aegon II's youngest brother, was also killed. The riderless Tessarion, Daeron's dragon, rose into the sky and Addam fought them. However Hugh's dragon Vermithor then began attacking the men on the ground. Addam fought them, According to Archmaester Gyldayn, Addam must have felt duty bound to protect his men on the ground, though surely knew Seasmoke could not defeat the older dragon. Tessarion joined the battle and all three dragons fell to the ground and fought to the death, in which Addam was killed.
The losses in the battle meant that the Green Commander Lord Unwin Peake ordered a retreat from Tumbleton, after Ulf was poisoned for trying to claim rule himself. Despite being accused of being a turncloak, Addam had saved King's Landing at the cost of his life.
In 138 AC, from Raventree Hall the bones of Addam were returned to Driftmark. His brother
Alyn, now Lord of Driftmark, put only the word LOYAL as the Tomb's epitaph.