Seleucus in Harpers Dictionary of Classical Antiquities (1898)
Eldest son of Demetrius II., assumed the royal diadem on learning the death of his father, 125; but his mother, Cleopatra , who had herself put Demetrius to death, was indignant at hearing that her son had ventured to take such a step without her authority, and caused Seleucus also to be assassinated.
Seleucus IV Philopator in Wikipedia
Seleucus IV Philopator (Greek: Σέλευκος Δ' Φιλοπάτωρ), ruler of the Hellenistic Seleucid Empire, reigned from 187 BC to 175 BC over a realm consisting of Syria (now including Cilicia and Judea), Mesopotamia, Babylonia and Nearer Iran (Media and Persia). He was the second son and successor of Antiochus III the Great and Laodice III. The wife of Seleucus IV was his sister Laodice IV, by whom he had three children: two sons Antiochus, Demetrius I Soter and a daughter Laodice V.
He was compelled by financial necessities, created in part by the heavy war-indemnity exacted by Rome, to pursue an ambitious policy. In an effort to collect money to pay the Romans, he sent his minister Heliodorus to Jerusalem to seize the temple treasury. On his return, Heliodorus assassinated Seleucus, and seized the throne for himself.
The true heir Demetrius, son of Seleucus, was now being retained in Rome as a hostage, and the kingdom was seized by the younger brother of Seleucus, Antiochus IV Epiphanes. Antiochus managed to oust Heliodorus and an infant son of Seleucus, also named Antiochus, was formal head of state for a few years until Epiphanes had him murdered.
Seleucus V Philometor in Wikipedia
The Seleucid king Seleucus V Philometor (126 - 125 BC), ruler of the Hellenistic Seleucid kingdom, was the eldest son of Demetrius II Nicator and Cleopatra Thea. The epithet Philometor means mother-loving and in the Hellenistic world usually indicated that the mother acted as co-regent for the prince.
In 126 BC Demetrios II was murdered at the instigation of his wife Cleopatra Thea. Now she herself took power and soon also killed her oldest surviving son Seleucus V. Two different motives are given as reason for this deed: According to one version he had attempted to claim the throne without her agreement, according to the other version she was afraid that he might avenge the assassination of his father.