Today at the NYCC 2017 Lucasfilm Publishing Panel Timothy Zahn announced that he will be following up this years novel Star Wars: Thrawn with a sequel titled Star Wars: Thrawn Alliances featuring Darth Vader! #BlackandBlue
To my knowledge Thrawn and Vader didn't have significant interactions in the Legends stories and we have yet to see them cross paths on Rebels but they have met in the new Star Wars canon (Star Wars: Thrawn). I’m very excited for Timothy Zahn to continue the story of Thrawn and explore the dynamic of an Empire with Thrawn, Vader, Tarkin, and Krennic all vying for the Emperor's favour. Expect the new book to hit shelves in summer of 2018!
We are going to see Thrawn next in the final season of Star Wars: Rebels kicking off on October 16th and in the six-issue comicbook adaptation of Star Wars: Thrawn coming this February.
Thanks for reading,