
Brian Herbert was born June 29, 1947, so he turned 12 in 1959.
Frank Herbert has been working on the book that would become Dune, and around 1959 he decides to add another character: Duke Leto's 12-year-old son, Barri. He soon changes the name to Paul, but notice the similarity of the original names: Brian, Barri…
Frank gets stuck on the writing until he fires his agent in November 1961. After that he makes quick progress over the following months, writing and revising throughout 1962 and into 1963. Brian turns 15 in 1962, and in the early drafts of the first chapter, presumably written around this time, we see that Frank changes Paul's age, from "almost twelve" to "already fifteen."
Coincidence? Hardly!
There is only one explanation: Brian Herbert is the Kwisatz Haderach!
(Still, one must ask: What is the son but an extension of the father?)