Circa 2358, he and Counselor T'Pelak invigilated Cadet Tasha Yar in the Priam IV test, a holodeck training simulation designed to test how Yar considered Prime Directive issues and handled decisions regarding them. Forbus and T'Pelak hypnotized Yar into believing the simulation was real.
They took part in the early stages of the test, pretending to be cadets with Yar on the USS Threnody. The three escaped its destruction in an escape pod but crash-landed on Priam IV. Forbus's character was crushed and killed in the crash.