The upcoming movie will draw a line under the Skywalker saga and form the ending of the current so-called sequel trilogy.
Unsurprisingly, JJ Abrams’ plot details are being kept strictly under wraps – and Gleeson is terrified that after reading the script, he’ll give away the shocks that are in store.
Speaking on the Happy Sad Confused podcast, he teased: “I made the terrible mistake of reading the script. I know everything.”
Now it seems the challenge for him for the next year-and-a-quarter will be keeping everything under wraps.
“The nightmare is falling asleep on public transport,” he joked.
“The nightmare is you wake up on a plane and someone’s dictating. You wake up and your mouth is shaping words, you wake up and you’re like ‘Skywalker did this.’
“And then you realise you don’t know how long you’ve been speaking, and there’s a kid filming, there’s somebody writing it down.
“And because you’re in the air, you say, ‘We need to have a talk before we land, I can access my bank account.’”
Gleeson will be back as General Hux in Episode 9, which is now in production.
He previously spoke out about fears of a potential fan backlash to his character – which, generally speaking, never happened; despite a small but incredible vocal resistance to the events of The Last Jedi by some fans.
“I felt a little worried about fan reaction, but you can’t control that – all you can do is your job,” he told Entertainment Weekly.
“General Hux is ridiculous in lots of ways, but not in a hilarious way.
“But just anything to do with that level of… what’s the word? Pomp and all the rest of it, the higher reigns of military, all the badges and the medals.
“At a certain point you say, ‘Why is that man wearing that hat? That doesn’t make him more powerful.'”
Dominic Monaghan and Matt Smith have recently been added to the line-up for the next film, alongside fellow newcomers Keri Russell, Richard E Grant and Naomi Ackie.
Star Wars: Episode 9 is out in December 2019.