What Downey does not mention is that Odenath (and his son by a previous marriage) appears to have been murdered in Antioch, showing how the city had become one of the dual poles of Palmyrene power. Gayle Young in here thesis "WORTHY WARRIOR QUEEN:PERCEPTIONS OF ZENOBIA IN ANCIENT ROME", Georgetown University, Washington, D.C., 2009 maintains:
"...Odaenathus did not have long to savor his remarkable victories or his elevation to King of Kings. He was killed shortly afterwards in Antioch by a relative, along with his elder son and heir, Herodes. There was some speculation in the ancient histories that the Emperor Gallienus, becoming fearful of the Palmyra’s military might, conspired to have Odaenathus secretly assassinated. The inconsistent SHA* first blames the king’s death on revenge by Persian gods, but then states that it was a conspiracy orchestrated by Zenobia to ensure that her son, rather than Herodes, inherited the throne. Zonaras, writing in the 12th century from sources now lost to us, has the most credible version of the murder, stating the royal father and son were killed by the king’s disgruntled nephew who had been punished for misbehaving during a family hunting expedition". Apparently, Zonaras contends that, while hunting with the king, the nephew killed beasts before the king had a chance to do so - a breach of etiquette that led to his brief imprisonment. When he was released, the nephew killed the king and Herodes with a sword during a family dinner.
* Scriptores Historiae Augustae, Volume III: The Two Valerians, The Two Gallieni, The Thirty Pretenders, The Deified Claudius, The Deified Aurelian. Translated and edited by David Magie. Cambridge: Loeb Classical Library, 1932.