So naturally, this is the first topic that come up during one of Gleeson's first major press appearances since getting cast in "Star Wars," when part of the "Harry Potter" cast attended the media opening of The Wizarding World of Harry Potter's Diagon Alley theme park expansion at Universal Orlando.
Gleeson's self-imposed gag order is so intense, in fact, that when asked at a press conference about "Star Wars," the actor started laughing as soon as one member of the media got halfway through the word "star," merely shouting, "No! No! I can't."
When MTV News sat down with the actor right under a fire-breathing dragon perched on top of Gringotts Bank in Diagon Alley, he wasn't necessarily more forthcoming about what he'll be doing in the sequel, but he was able to open up on his trepidations about joining another major franchise.
"I'm a pessimist by nature, so it's always the worst things that come to mind first, whenever you make a decision, or have a decision to make," Gleeson said. "So of course, yeah, you worry the way it will disrupt the way you live your life."
Though Gleeson's role as Bill was only in the last two parts of the "Harry Potter" saga, it's his highest profile role to date, and certainly one that should make him recognizable all over the world. But instead, "Harry Potter" is exactly the reason Gleeson felt comfortable jumping into "Star Wars."
"The truth of the matter is, I was in 'Harry Potter' and I can walk in the street and no one bothers me," Gleeson continued. "It's totally fine. The only reason I'm doing 'Star Wars' is because the script is great, because J.J. [Abrams] is great, and because the cast are great. And that's what you look for in any movie. So in a way, it's just another job."
Sure, just another mega-budget job on a blockbuster movie with the expectations of the world on his shoulders. So no big deal, right? Wrong, of course, and though Gleeson doesn't expect to get mobbed at the grocery store, he does know his spoiler policy has the potential to effect him in an even greater way.
"I could destroy my life if I gave away one of the secrets, really quickly," Gleeson said. "I'm just always with a no-talk policy about it."
More than just the potential to completely obliterate his burgeoning career, Gleeson has another reason for keeping his mouth shut.
"I enjoy going to a film and being surprised, maintaining that is an important thing generally," Gleeson noted. "I'm going to keep my mouth shut until the movie is all the way out and on DVD. So I don't upset anyone."
That's in stark contrast, perhaps, to fellow cast-member John Boyega. Boyega hasn't necessarily revealed anything, as far as we know; but he has tweeted the fan-baiting phrase "Skywalker" previously from Twitter, something that made Gleeson double over with laughter when he found out.
"I wonder if he has to put them by lawyers before he puts them out there!" Gleeson said, laughing. "I wonder!"
In one last ditch effort to get Gleeson to spill anything, we asked if the beard he was sporting was in any way was related to the beard Mark Hamill (Luke Skywalker) announced he had grown for "Episode VII." Sadly, our follicular detection yielded nothing.
"No," Gleeson said when asked if he was sporting a perhaps Jedi-inflected beard, "but I haven't been on set for a couple of weeks, so that doesn't give anything away."
Gleeson may not have time to spill "Star Wars" spoilers anyway. Besides appearing in his biggest "Harry Potter" roll to date in the "Escape From Gringotts" ride, he just finished a movie called "Brooklyn" working with Saoirse Ronan, reteamed with "Star Wars" co-star Oscar Isaac for Alex Garland's sci-fi movie "Ex Machina," appears in "Unbroken" directed by Angelina Jolie at Christmas, has a movie with his father Brendan Gleeson called "Calvary" hitting stateside shortly, and is in a crazy sounding movie called "Frank" with Michael Fassbender and Maggie Gyllenhaal.
"It's about a guy who joins a band, and the lead singer of the band has a giant Papier-mâché head he never takes off," Gleeson said. "That guy is played by Michael Fassbender. The music is great, the comedy is great, and I think it's pretty entertaining and deep, you know?"
And if that wasn't enough, Gleeson would be more than willing to hop back on his broomstick for more "Harry Potter," even though he had only heard about the "Fantastic Beasts" spin-off the night before.
"Oh, if they ask, I'm there," Gleeson said. "It's set 80 years before so I won't be doing a cameo any time soon. But I'll certainly put on a beard and pretend to be a Weasley from 80 years ago, absolutely, I'd love that."
The Wizarding World of Harry Potter — Diagon Alley opens on July 8. "Star Wars: Episode VII" opens December 18, 2015, more than enough time to ride "Escape From Gringotts" a few times while you're waiting.