Adapted from an English translation of Dio’s Roman History, Book 78, by Earnest Cary PhD, 1914, taken from the LacusCurtius website.
After this Antoninus assumed the entire power; nominally, it is true, he shared it with his brother, but in reality he ruled alone from the very outset. With the enemy he came to terms, withdrew from their territory, and abandoned the forts; as for his own people, he dismissed some, including Papinian, the prefect, and killed others, among them Euodus his tutor, Castor, and his wife Plautilla, and her brother Plautius. Even in Rome itself he killed a man who was renowned for no other reason than his profession, which made him very conspicuous. I refer to Euprepes the charioteer. He killed him because he supported the opposite faction to the one he himself favoured. So Euprepes was put to death in his old age, after having been crowned in a vast number of horse-races; for he had won seven hundred and eighty-two crowns, a record equalled by no one else. As for his own brother, Antoninus had wished to slay him even while his father was still alive, but had been unable to do so at the time because of Severus, or later, on the march, because of the legions; for the troops felt very kindly toward the younger brother, especially as he resembled his father very closely in appearance. But when Antoninus got back to Rome, he killed him also. The two pretended to love and commend each other, but in all that they did they were diametrically opposed, and anyone could see that something terrible was bound to result from the situation. This was foreseen even before they reached Rome. For when the senate had voted that sacrifices should be offered on behalf of their concord both to the other gods and to Concord herself, and the assistants had got ready the victim to be sacrificed to Concord, and the consul had arrived to superintend the sacrifice, he could not find them and they could not find him, so they spent nearly the entire night searching for one another, and so the sacrifice could not be performed then. And on the next day two wolves went up to the Capitol, but were chased away from there; one of them was found and slain somewhere in the Forum and the other was killed later outside the pomerium. This incident also had reference to the brothers.
Antoninus wished to murder his brother at the Saturnalia, but was unable to do so; for his evil purpose had already become too obvious to remain hidden, and so there now ensued many sharp encounters between the two, each of whom felt that the other was plotting against him, and many defensive measures were taken on both sides. Since many soldiers and athletes, therefore, were guarding Geta, both abroad and at home, day and night, Antoninus induced his mother to summon them both, unattended, to her apartment, with a view to reconciling them. Geta was persuaded, and went in with him, but when they were inside, some centurions, previously instructed by Antoninus, rushed in a body and struck down Geta, who at the sight of them had run to his mother, hung about her neck and clung to her bosom and breasts, lamenting and crying: ‘Mother who bore me, mother who bore me, help! I am being murdered.’ And so she, tricked in this way, saw her son perishing in the most impious fashion in her arms, and received him at his death into the very womb, as it were, from where he had been born; for she was all covered with his blood, so that she took no notice of the wound she had received on her hand. But she was not permitted to mourn or weep for her son, though he had met so miserable an end before his time (he was only twenty-two years and nine months old), but, on the contrary, she was compelled to rejoice and laugh as though at some great good fortune, so closely were all her words, gestures, and changes of colour observed. Thus she alone, the Augusta, wife of the Emperor and mother of the Emperors, was not permitted to shed tears even in private over so great a sorrow.