Elagabalus

On June 8, 218, Elagabalus became the emperor of Rome. From the article:

On June 8, 218 CE, Macrinus and his forces were defeated by the Roman commander Gannys outside Antioch. The fallen emperor's failed attempt to cross the Bosporus at Cappadocia and escape to Rome would bring about his (and his nine-year-old son's) death. Macrinus's death and the claim that Elagabalus was actually Caracalla's son would be enough for the Roman Senate to accept him as the new emperor - the youngest to ever sit on the throne; official recognition would not come until his arrival in Rome. However, instead of leaving immediately, the new emperor, his mother and grandmother would winter at Nicomedia before arriving in Rome in the autumn of 219 CE. Unfortunately for the man who had defeated Macrinus, Gannys would not get to see his young protégé seated on the throne. By some accounts he had been not only a protector but a father-figure to Elagabalus whilst others claim he was either a eunuch or Julia Soaemis' lover. Whatever his relationship to the family may have been, his closeness to the young emperor meant that he remained a threat to a controlling mother and grandmother, and this threat led to his death."