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Explanation: When the Emperor Pertinax took the throne, he declined to name his wife Empress or his son his heir. This was probably to spare them in case he was overthrown - which he, sadly, was. This was successful! Both his wife and his son survived his assassination, and the next Emperor, Septimius Severus, did not appear to regard either as threats to his legitimacy.
Septimius Severus had two sons, who he elevated as his heirs - Geta and Caracalla. When Septimius Severus died, Caracalla shortly thereafter murdered Geta, leaving him to die in the arms of their mother, despite his mother specifically requesting he not murder his brother ๐ญ
Pertinax the Younger, the aforementioned son of Pertinax, apparently took this opportunity to joke that Caracalla should take the victory title 'Getacus' - meaning, roughly, 'Conqueror of Geta', in the spirit of traditional victory titles like 'Germanicus' ('Conqueror of Germania'), 'Parthicus' ('Conqueror of Parthia'), 'Britannicus' ('Conqueror of Britannia'), etc. Other than mocking Caracalla's petty murder of his brother by comparing it to great deeds, it also highlighted that Caracalla had very few military accomplishments to his name, despite deeply craving the approval of the soldiery.
Pertinax the Younger did not long survive this joke, for obvious reasons.