Aelius Antipater
In his orations , both extempore and written , some of which are mentioned by Philostratus , Antipater was not superior to his contemporaries , but in the art of writing letters he is said to have excelled all others , and for this reason the emperor Severus made him his private secretary and tutor ( "ab epistulis" ) of his two sons Caracalla and Geta . 
<triplet> Caracalla <subj> Geta <obj> sibling <triplet> Geta <subj> Caracalla <obj> sibling