Sometime after arriving on Exo III in 2261, with Ruk's help and with the records he could find, Korby constructed an android copy of Brown. In 2266, Chapel evidently felt Brown's reaction to seeing her was less than she expected; when Kirk noted this, she attributed it to five years spent in the dark ruins of Exo III.
Korby did not wish for Kirk to communicate with his ship. To prevent him from doing so, Brown threatened him with a phaser, and during a brief scuffle that followed, Brown was shot at close range, damaging him enough to render him inert.
Events at Exo III ultimately revealed that android copies of living beings weren't the precise duplicates Korby believed; this may have accounted for Brown's reduced emotional response to Christine Chapel, and his somewhat simplistic behavior. (TOS: "What Are Little Girls Made Of?")