Popular in Austin, Texas, since the mid-1970s, as a variant of "hello". It is part of what is referred to as krelltalk, which originated after a group of Austinites saw a UFO while tripping
in the mid 1970s and encountered an extraterrestrial. The alien recalled the movie "Forbidden Planet" and the extinct alien species, the Krell. Thereafter, krello became a substitute for hello and krellwell became a substitute for farewell

Someone who used to be a potential girlfriend/boyfriend, but no longer is.