Sir Charles Alexander Petrie, 3rd Baronet (28 September 1895 – 13 December 1977) was a British historian.
Born in Liverpool, he was the younger son of Sir Charles Petrie, 1st Baronet and his wife Hannah. He was educated at the University of Oxford, and in 1927 succeeded to the family baronetcy.
Petrie was known for his interest in royalism and Jacobitism, and particularly for his 1926 essay in counterfactual history, If: A Jacobite Fantasy, in which Bonnie Prince Charlie went on from Derby to Oxford (albeit to a cool reception), but just as all seems lost, the Duke of Newcastle appears in haste to tell him that George II, head of the Hanoverian dynasty has fled back to Hanover, and to belatedly declare his loyalty. (It has been speculated by some historians that Newcastle, known to have flirted with Jacobitism, actually was contemplating a judicious "conversion" to the Stuart cause when the Prince's army reached Derby.) As a result, large elements of the people and army came over to the Stuart side, and there was never the disastrous retreat and thus, there was never a Battle of Culloden in 1746, all leading to a Jacobite restoration,and the successive reigns of James III (The Old Pretender), Charles III, Henry IX and the continued tenure of the House of Stuart until the twentieth century. It also depicts the American Revolution as not taking place because of the judicious intervention of Charles Edward, and Washington going on to become a great British general, and other flights of fantasy.
Several of Petrie's books deal with Charles I's government, towards which he was broadly sympathetic. He published biographies of Lord Bolingbroke, of the early-20th-century British cabinet minister Walter Long, and of three Spanish kings: Philip II, Charles III, and Alfonso XIII. Another biography of his dealt with a fourth notable Spaniard: Philip II's half-brother Don John of Austria.