Or specifically its the big reveal at the end of Book 1 Dune Book 1, which is broken into 3 books, and is the opening phrase of Book 2, which begins with Paul saying 'Now Harkonnen shall kill Harkonnen.' right before Duncan Idaho finds them and picks them up to take to Liet Kynes.
of course not. I did have to double-check because I initially wanted to reference the grandmothers but neither is discussed in the original book at all and barely get any mention in the original series, its still debatable if Gaius Mohiam was actually intended by FH to be Paul's grandmother or if KJA & BH just decided to got that route. In any event, fair question, I ended up looking up the grandfather to be sure and its a major feature of the original book.
- Albert Einstein
King of Cairhien 20-7-2
Chancellor of the Landsraad, Archduke of Is'Mod