Kirk's brother was portrayed by William Shatner. It's a little surprising that he went to the trouble, rather than just have a handsome background actor lie there for the shot. Anyway, it was good continuity with WALGMO. I was extremely irked in STAR TREK V when Kirk says "I had a brother once", and it turned out to be a mere rhetorical flourish in film that had no memory of actual Star Trek. Zero research, crap writing. Bjo Trimble had already published the research: all they had to do was open the Concordance and flip to the page for Kirk. They couldn't be bothered