From 1730, Sempill became one of the most prominent and active Jacobite agents in France, and acted as the unofficial Stuart ambassador to
Louis XV at Versailles after the Stuarts were forced to leave France for Rome due to the
Anglo-French Alliance. Reflecting the confused nature of Jacobite politics at the time, Sempill worked alongside, and sometimes against,
Daniel O'Brien and
George Kelly who had also been commissioned to represent Stuart interests in France. Such was Sempill's conviction that
Prince Charles Stuart travelled to Paris, where he stayed at Sempill's house on the
rue de l'Estrapade. The planned French expedition was, however, abandoned in the summer of 1744, by which time Prince Charles had lost trust in Sempill and publicly mocked him as "Lord Simple". Sempill was excluded from Prince Charles's plans for a new rising, but he subsequently worked to persuade Louis XV to mount an invasion during the 1745 rising. His efforts were embarrassed by the failure of England to rise in support of the rising and ended with Jacobite defeat at the
Battle of Culloden. By this stage, Sempill had also lost the confidence of James Francis Edward Stuart. He had married Lady Mary Caryll, widow of Hon. John Caryll and daughter of
Kenneth Mackenzie, 4th Earl of Seaforth. Sempill died in 1748, isolated from the Jacobite court. ==References==