At C2E2 in Chicago this week, Del Rey and Marvel have revealed an accompanying prequel novel and 3-issue comic series to tie-in with upcoming Star Wars spin-off movie Rogue One.
Del Rey's Elizabeth Schaefer announced the prequel novel for Rogue One will be called Catalyst and will release in the fall of this year, but sadly this is all we know so far as an unfinished cover was shown and the author's name remains a mystery.
Schaefer also revealed a bit of information about July's upcoming second instalment of the Aftermath trilogy, Aftermath: Life Debt - "Before Han can settle down with Leia, he has one last debt to pay. This is a story of our favorite BFFs on Chewie's home planet." She also mentioned that Claudia Gray's novel Bloodline, set before The Force Awakens, focuses on Leia and her role in the New Republic and the rise of the Resistance.
Marvel also announced a 3-issue comic series plus a one-shot in October that will provide further backstory for Rogue One.
Rogue One: A Star Wars Story