During the battle of Diortem, Sepp sent the ISA a message from his embassy. The message was concerning the kidnapping of ISA Admiral Alex Grey. Sepp told the ISA of her whereabouts, which led to the Phantom Talon Corp saving her.
Some time later, Sepp's embassy came under siege from Helghast forces. Unknown to Sepp, the Helghast wanted his son, who had been implanted with a code that had the potential to activate a deadly virus. Sepp and his wife Valeria were killed in the ambush, to Grey's disappointment.