Big Crane on Campus (season 7) Frasier has Lorna overnight. In the morning, she calls home yelling, "Put your brother on!!!"

Is Kirby's brother ever mentioned after this episode?

I remember that but I don't think they mentioned him anymore after that. How weird....

Season 8: Semi-Indecent Proposal

Frasier: So, how are those kids of yours doing?
Lana: Oh, my youngest is good, he's in the ninth grade. But Kirby,
if he doesn't pass U.S. history he's not going to graduate.
Frasier: Well, have you considered getting a tutor?