Antiochus Grypus was crowned as a teenager in 125 BC after his mother Cleopatra Thea had killed his elder brother Seleucus V Philometor, ruling jointly with her. After Antiochus defeated usurper Alexander II Zabinas in 123 BC his mother tried to poison him with wine, but the suspicious king forced her to drink the cup herself. (The story may have been inspired by the fact that Grypus was interested in toxicology; some poems about poisonous herbs believed to have been written by him are quoted by the famous physician Galen).
Either he or his half brother Antiochus IX Cyzicenus is probably identical with the ephemeral child ruler Antiochus Epiphanes, who was crowned by Cleopatra Thea after the death of Antiochus VII but before Demetrius II returned to Antioch. The child Antiochus Epiphanes, who is known from coins, was deposed—but not killed—when Demetrius II was restored in 129 BC.