Douglas was summoned to Stirling Castle, under a safe conduct by the King, who requested his aid against the rebellious Earls of Crawford and Ross. However, Douglas had signed a bond with these earls and refused to support the King, who responded by stabbing Douglas. He was then attacked and killed by the King's retainers, and his body thrown from a window. The siege of Threave William's brother James Douglas, now 9th Earl, hastily continued the additions to Threave, completing the artillery house as well as earthworks to the north of the keep. After his brother's murder, he intrigued with the English court, receiving money from Henry VI's government for the works. The 9th Earl's uprising was defeated at the Battle of Arkinholm near Langholm on 1 May 1455, following which his strongholds were systematically besieged. Threave Castle was the last castle to fall, and the royal forces arrived in June. King James resided at Tongland Abbey during the siege, which lasted over two months. The new artillery house prevented the King's men from taking the castle by force, even when a bombard, a large siege cannon, was brought up from Linlithgow Palace at a cost of over £59. Instead, King James persuaded the garrison to surrender by making payments and grants of land to Douglas supporters. One myth associated with the siege, which is related by Nigel Tranter, is that the great cannon Mons Meg was built in Kirkcudbright by a smith named Mollance. The cannon was then presented to James II and employed in the siege of Threave. The myth goes that the first cannonball smashed right through the castle, taking off the Fair Maid's hand as she drank. However, it is known that Mons Meg was actually made in Burgundy and arrived in Scotland until 1454. Royal fortress The castle, along with the lordship of Galloway, was annexed by the Crown, and a succession of keepers were appointed. James II returned in 1460, on his way to the siege of Roxburgh Castle, where he would be killed by an exploding cannon. James III gave the castle to his wife Margaret of Denmark, though it is not known if she ever visited. James IV visited in 1502, when royal accounts record cloth, wine and falconers being brought to Threave. In 1513, Robert Maxwell, 5th Lord Maxwell, was appointed keeper following the death of the previous keeper, John Dunbar