It does not seem possible that Alexander Helios the eldest son of Cleopatra by Antony could have been old enough to play any significant role in the rivalry between Antony and Octavius/Augustus. Cleopatra was 28 years old when she became the permanent partner of Antony.
It is conceivable, even probabable, that she had become a mother in her mid-teens as was the custom. In other words, her son by Caesar was not likely her firstborn child.
Antony also agreed to marry Alexander Helios to the daughter of the King of Media. If born in 44 BC he would have been less than 10 years old at the time of this arrangement, at least by present accounting. According to Roman law a male had to be 15 years old to be married, but royal marriages or betrothals were evidently exempt.
All things considered, the "older" brother of Herod the Great named Phasaelus was probably not one and the same as Alexander Helios. He or Ptolemy Philadelphus could still have been the younger brother of Herod named Pheroras. And it is still possible that Phasaelus was one and the same as Marcus Agrippa, but this needs more study.
I've been looking at various genealogies of the Julio-Claudian dynasty. There is a lot of confusion. As in the royal dynasties of pharaonic times, parentage of royal children is very much guarded and therefore ambiguous.
The father of Herod the Great was supposedly poisoned to death in 43 BC. If Antony was the true father of Herod the Great, and this still seems to be the best reason for his favor with Antony, then the poisoning of Antipater has to be explained. For example, was Jewish identity of Antony as "Antipater" no longer useful to him, and therefore "killed off". Or did Herod have more than one father figure in his life, as was so common in earlier pharaonic times when a prince typically had a biological father, a legal father, and a political father?
© Charles N. Pope, US Library of Congress. All rights reserved.