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|Alias||The Mad Heir|
|Born||In or before 107 AC|
|Died||In or after 136 AC|
Arnold twice rose against his cousin to contest her inheritance, claiming that women were too soft to rule. After his second rising sometime before the Dance of the Dragons, he was imprisoned in one of the sky cells of the Eyrie.
Jeyne died in 134 AC. In her last testament, she named her fourth cousin, Ser Joffrey Arryn, as heir, though Arnold was much closer by blood. Though Arnold had gone mad during his time imprisoned in the sky cells, his sane, shrewd, and ambitious son, Ser Eldric, came forward to press his father's claim. Many lords supported Arnold's claim, insisting that the laws of inheritance could not be put aside by "the whim of a dying woman." Additionally, a third claimant came forward in the person of Isembard Arryn, head of House Arryn of Gulltown.
Ser Corwyn Corbray, one of the regents of young King Aegon III Targaryen, ruled that Jeyne's will must prevail and declared Joffrey the rightful Lord of the Eyrie. Isembard and his sons were imprisoned and Eldric was executed, but Arnold eluded Corwyn and fled to Runestone. When Corwyn arrived at the castle, a crossbowman of Runestone killed Corwyn after he drew Lady Forlorn against Lord Gunthor Royce, Arnold's protector.
Striking down the king's regent was an act of treason, and war began anew across the Vale of Arryn. Houses Royce, Templeton, Tollett, Coldwater, Dutton, and the lords of the Three Sisters supported Arnold's claim, though the Hand of the King, Lord Thaddeus Rowan, commanded the lords supporting Arnold to lay down their arms. When no reply was forthcoming, the crown sent men through the Mountains of the Moon and launched a sea attack to support Joffrey's claim.
By the time the new regents were chosen by lot in 136 AC, Lord Alyn Velaryon and Lord Benjicot Blackwood had at last forced the supporters of Isembard and Arnold to do homage to Lord Joffrey as their liege.