Tom Holland writes (p 360) in Rubicon:
"Young Alexander [Helios], garbed as a Persian king of kings, was promised Parthia and all the realms beyond it."
This is clear indication that the king of Ptolemaic Egypt, which Marc Antony had clearly become, had the traditional right to appoint the kings of Parthia! This also marks Roman advancement from implicit to explicit kingmakers in Egypt. That is, Marc Antony was no longer content to produce a firstborn child on Cleopatra to be adopted by a Ptolemaic prince as future heir to the Egyptian throne, but he entered into a formal marriage with Cleopatra as present king of Egypt.
© Charles N. Pope, US Library of Congress. All rights reserved.