In exile Cameron remained in Prince Charles's service, travelling with him to Madrid in 1748 and returning to Scotland privately in 1749. In 1753 he was sent back to Scotland again to obtain money from Loch Arkaig and to participate in a desperate plot to assassinate George II and other members of the British royal family. However, while he was staying secretly at Brenachyle by Loch Katrine, he was betrayed by MacDonell of Glengarry, the notorious "Pickle the spy", and members of his own clan who by this time were sickened by his Jacobitism. He was arrested and attainted of high treason under the Attainder of Earl of Kellie and Others Act 1746  for his part in the 1745 uprising. He was imprisoned in Edinburgh Castle then taken to Tower Hill in London. On 7 June 1753 Cameron was drawn on a sledge to Tyburn and hanged for 20 minutes before being cut down and beheaded. His remains were buried in the Savoy Chapel, Westminster. He was the last Jacobite to receive the death penalty. In his final papers, written from prison, he still protested his undying loyalty to the Jacobite cause and his episcopalian principles. In 1753 John Cameron of Dochanassie composed "A Song to Doctor Cameron", a song in Gaelic in commemoration of Cameron's life. Cameron is a leading character in D. K. Broster's novel The Gleam in the North , the second in her Jacobite trilogy.. How many years passed that Cameron traveled with Prince Charles to Madrid and returned to Scotland?