Earlier today The Star Wars Show revealed a first look at the upcoming Thrawn: Alliances novel. The cover features Thrawn with none other than Darth Vader himself.
Not much is known about the novel other than the fact that Vader works with Thrawn. The book is written by Thrawn creator, Timothy Zahn, who also wrote the first Thrawn novel. The book is slated to be released in June 2018, so I’m sure we’ll have more details by then.