Editing Cleopatra Thea (section)

===Co-ruler of Antiochus VIII===
[[File:Seleucidi, cleopatra tea e suo figlio antioco VIII, tetradracma, 121-120 ac.JPG|thumb|Coin of Cleopatra Thea and Antiochus VIII]]
Demetrius' elder son, Seleucus, proclaimed himself the new king with the name Seleucus V, but Cleopatra Thea had him executed by archers soon after. From 125 BC to 121 BC Cleopatra ruled Syria, sharing the throne with her son, [[Antiochus VIII Grypus]], whom she had proclaimed king in Antioch in 128 BC. Antiochus VIII was married to [[Tryphaena]], the daughter of Ptolemy VIII Physcon and Cleopatra III.<ref name="CB"/><ref>[http://www.tyndalehouse.com/Egypt/ptolemies/tryphaena_fr.htm Tryphanea] by Chris Bennett</ref> 
Cleopatra Thea thus procured an Egyptian alliance, causing Ptolemy to turn against Alexander II (whom he had previously supported as a means of keeping the Seleucids preoccupied with civil war). By 123 BC Alexander II had been defeated and executed, Cleopatra and Grypus remaining joint rulers in Cilicia, Syria and Northern Mesopotamia.

Grypus became less controllable as he grew up, and in 121 BC Cleopatra Thea decided to eliminate him. She offered him a cup of poisoned wine, but Grypus guessed her intention and forced her to drink the wine, which killed her.<ref name="CB"/> Grypus's sole reign was peaceful until ca. 114 BC, when Cleopatra Thea's other son, Antiochus IX, returned to Syria to claim the throne and civil war started again.