Titus Livius (Livy), The History of Rome, Book 40
Evan T. Sage, Ph.D. and Alfred C. Schlesinger, Ph.D., Ed.

54. The same year¹ Philip, king of the Macedonians, died, broken down by age and grief at the death of his son. [2] He was wintering at Demetrias, [p. 165]distressed both by longing for his son and by² repentance³ of his own cruelty. [3] His mind was further disturbed, firstly by his other son, who was already and beyond doubt the king, both in his own opinion and that of others, the eyes of all being turned upon him, secondly, by the loneliness of his own old age, since some were waiting for his death and others not even waiting for it. [4] All this caused him the more distress, as it did to Antigonus the son of Echecrates, who bore the name of his uncle Antigonus, the guardian of Philip, a man of regal dignity, and renowned also for the famous battle against Cleomenes the Lacedaemonian.⁴ [5] The surname “the guardian”⁵ was given him by the Greeks to distinguish him from the other of that [6] name. The younger Antigonus, the son of his brother Echecrates, of all the friends whom Philip had honoured, alone remained uncorrupted, and this loyalty to Philip had made Perseus, under no circumstances a friend, a most deadly [7] foe. Foreseeing in his mind with how great danger to himself the inheritance of the kingdom would fall to Perseus, as soon as he saw that the mind of the king was wavering and that he sometimes grieved at the loss of his son Demetrius, now by listening to him, now by even provoking him to talk of that rash act, with laments of his own he echoed the laments of [8] Philip. And while the truth, as usually happens, was offering many foretokens of itself, he aided with all his might in bringing everything to light with greater [9] speed. Suspicion had fallen particularly upon Apelles and Philocles as the instigators of the crime, since they had been the ambassadors to Rome and had brought [p. 167]the letter, fatal to Demetrius, which bore the name⁶ of Flamininus.