Flavius Josephus, The Wars of the Jews
William Whiston, A.M., Ed.

[72] But vengeance circumvented him in the affair of his brother Antigonus, whom he loved, and whom he made his partner in the kingdom; for he slew him by the means of the calumnies which ill men about the palace contrived against him. At first, indeed, Aristobulus would not believe their reports, partly out of the affection he had for his brother, and partly because he thought that a great part of these tales were owing to the envy of their relaters: however, as Antigonus came once in a splendid manner from the army to that festival, wherein our ancient custom is to make tabernacles for God, it happened, in those days, that Aristobulus was sick, and that, at the conclusion of the feast, Antigonus came up to it, with his armed men about him; and this when he was adorned in the finest manner possible; and that, in a great measure, to pray to God on the behalf of his brother. Now at this very time it was that these ill men came to the king, and told him in what a pompous manner the armed men came, and with what insolence Antigonus marched, and that such his insolence was too great for a private person, and that accordingly he was come with a great band of men to kill him; for that he could not endure this bare enjoyment of royal honor, when it was in his power to take the kingdom himself.