This post contains spoilers for Frank Herberts Dune Messiah.Paul Atreides wasnt the only one sad to see Duncan Idaho die while battling Sardaukar troops in Dune. Audiences also mourned the loss of Idahos performer Jason Momoa, whose carefree attitude lightened the sometimes too-heavy mood. While everyone else is brooding about prophecies and land rights, Duncan Idaho is making fun of Pauls skinny little arms.So those same fans are probably thrilled to hear a report from insider Jeff Sneider, who indicated that Momoa has joined the cast of Dune 3, which director Denis Villeneuve hopes to start filming this summer.Readers of the Frank Herbert books are probably also thrilled. But were not surprised. After all, we know that Idaho returns in some form or another throughout Herberts original series, most importantly in the second entry Dune Messiah, which will form the basis of Dune 3.A smaller-scale story focused on palace intrigue, Dune Messiah follows a conspiracy against Paul Atreides, who has become the Emperor of the Known Universe and currently leads a bloody Freman jihad against all who oppose him. The conspirators launch several attacks against Paul, the most powerful being a gift given to him by the technology-focused Bene Tleilax. The provide Paul with a ghola or clone of Duncan Idaho, who now goes by the name Hayt.Ghola play important roles in Herberts later books, but this is an early incarnation, which lacks a certain quality of the more advanced version. Hayt has no memories of his life as Duncan, and thus approaches Paul with the awareness that the two once meant much to one another, but not with the same emotional connection. Moreover, Hayt has been trained as a mentat or human computer, and serves in Pauls court as an advisor.Throughout Dune Messiah, Paul struggles to reconcile his love for Duncan with his reasonable mistrust of the Bene Tleilax and Hayt, compounded by the fact that Hayt tells Paul not to trust him. Complicating matters is the fact that Hayt starts a romance with Pauls sister Alia, which itself is part of the conspiracys manipulations.For those trying to square this summary with what you know of Dune and Dune: Part Two, an objection might arise. Alia isnt even born when Hayt dies. Isnt she much younger than him?The short answer is, Yes. The long answer is also, Yes, but with qualifiers and context that provide varying degrees of comfort.Alia has become a teenager by the time of Dune Messiah, but Hayt has been developed to the age of Duncan at his death and, thus, is a grown man. However, the age gap between them isnt as pronounced as one would expect, especially since Alia has genetic memories, which gives her access to the memories of every one of her ancestors.The novel goes to lengths to describe Alia as wise beyond her years. But it also spends a bit too much time talking about adolescent physical urges, which Hayt has been designed by the conspirators to excite.Join our mailing listGet the best of Den of Geek delivered right to your inbox!Uncomfortable as that storyline is, its unlikely to appear in Dune 3 in such an icky form. Villenueve has already shown a willingness to veer from canon with Alia, as demonstrated by having her appear in a vision as played by Anya Taylor-Joy instead of a small child with the mind of an adult, which David Lynch did with Alicia Witt in his movie.Also, Jason Momoa will surely blow off any strangeness in the romance, once again adding some levity to Herberts story.Dune 3 begins filming in Summer 2025.