When the Multiverse was destroyed in the last incursion between Earth-616 and Earth-1610, Doctor Doom, with Beyonder's powers, recreated it in the form of Battleworld. Earth-92131 was recreated in the Westchester domain, ruled by Baron Kelly.
The Shadow King realized that in comparison to those other domains, Westchester was a fragile paradise, and set out to ensure its survival by any means. Using the cloned body of Professor X, the Shadow King became Cassandra Nova, and used his new identity to become a politician and establish the Bureau of Super-Powers.
At the Clear Mountain, Cassandra Nova used a form of psychotherapy called the "Mind Field" to brainwash those mutants who arrived to the institute and force them to live in harmony, Shatterstar was one of those mutants.
When the Ten-Sentinel and the Shadow King were defeated, he decided to join the X-Force.