Fox, who became Pitt's lifelong political rival, then joined a coalition with Lord North, with whom he collaborated to bring about the defeat of the Shelburne administration. When Lord Shelburne resigned in 1783, King George III, who despised Fox, offered to appoint Pitt to the office of Prime Minister. But Pitt wisely declined, for he knew he would be incapable of securing the support of the House of Commons. The Fox–North coalition rose to power in a government nominally headed by William Cavendish-Bentinck, 3rd Duke of Portland.