Rebels and Timothy Zahn's new novels.
the infamous Maul cameo at the end. Because of this, viewers are wondering if Thrawn will ever be on the big screen, but it won't happen in Episode IX.
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In an interview with Radio Times, Grant was asked about the prevailing hypothesis he is the live-action Thrawn and took the opportunity to debunk the rumor quite definitively:
I’m not playing the Star Wars character you just mentioned. I’m not allowed to tell you anything. Otherwise I would be fired. It’s a complete lockdown on any information whatsoever.
While Lucasfilm does like to play up the secrecy of their films, they aren't afraid to be transparent when it's called for. Some may recall Carrie Fisher's likeness would be recreated via CGI for Episode IX. It's nice to see the studio isn't a completely closed book, as this allows fans to adjust their expectations accordingly. Now, well before Star Wars 9 debuts, audiences know Thrawn isn't in it and they can move on to the next theory that catches their attention. Whenever something as massive as Star Wars is involved, there's no shortage of rumors to sift through.
In all likelihood, Grant is playing a new character, perhaps some sort of commanding officer for the First Order. The villains took heavy losses in Logan) and certainly fits the profile of someone who would make a convincing Imperial-type. Seeing him interact with Domhnall Gleeson and Adam Driver (who have their own compelling dynamic) in Episode IX would be a treat.
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Source: Radio Times