The second son of Antiochus VIII sought to avenge the death of his brother Seleucus VI at the hands of their cousin, Antiochus X. But less than 2 years later he was himself killed in trying to capture Antioch. His cause was taken up by his younger brothers, Philip I & Demetrius III, who succeeded in taking control of major portions of their cousin's realm, effectively dividing & diluting Seleucid power. 

References: Josephus, Antiquities 13.369.

Other online resources:

• Antiochus XI Epiphanes - Jona Lendering's brief biographical sketch [Livius: Articles on Ancient History].

• Antiochus XI Ephiphanes - entry in Wikipedia's web.