This week’s Legion -- the penultimate episode of Season 1 -- was a crucial episode for the series, as the identity of the show's main villain was confirmed to be the Shadow King from Marvel comics , while It was made very clear that yes, David Haller’s father is indeed Professor Charles Xavier. Oh sure, Xavier’s name wasn’t said, but all the signs were there if you knew what to look for, starting with a certain wheelchair glimpsed in a flashback and extending into the history lesson David received about the Shadow King and his father.

How a lifelong comic book geek reacts when Professor X's wheelchair suddenly is backed out of a crate right behind them on the set of Legion.

Legion: Exploring the Mutants on the X-Men-Based TV Show 6 IMAGES

Amber Midthunder as Kerry in Legion.

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I was on the set of Legion’s “Chapter 7” and while I didn’t learn everything that would happen ahead of time, I learned quite a bit, and it was clear a lot was going on in this episode. I must confess to being particularly excited when I got to see Xavier’s wheelchair - even though I wasn’t meant to see it! Amusingly, Legion crewmembers unpacked the chair from a crate right behind me, as I sat eating lunch, which was a secret I had to hold on to until now. As it turned out, this chair was the one used in X-Men: Apocalypse by James McAvoy, with the Legion producers being given their choice between pretty much every variation from the X-Men film series.As I mentioned in my initial story about my visit to the set , Legion’s first season was produced inside a single, massive, converted warehouse in Vancouver (Season 2 will move production to Los Angeles), meaning as you walked around, all sorts of work was simultaneously being done for various parts of the production. So while Dan Stevens lay filming in a confined space representing David’s mental coffin, Amber Midthunder was doing fight rehearsal nearby for the sequence where Kerry imagines she’s fighting deranged mental patients. Meanwhile, Aubrey Plaza was stopping by set to practice being in a harness for moments as the Shadow King (in his Lenny guise), while I also walked past the Clockwork mental hospital set in shambles from Syd’s journey though it, and the replica ice structure used to film scenes between Oliver and Cary the day before. Later in the day, as I was getting ready to leave, I'd see Rachel Keller and Bill Irwin begin to film the scene where Syd and Cary go into that stark white room, with the red chamber in the center.All of which is to say that everywhere you turned on the Legion set, there was something cool and imaginative to see.Stevens’ work on this busy day involved him playing both David and David’s “rational mind” (sporting a British accent, as Stevens does in real life) and on set, Stevens shot the British side first. Then, when he acted out the other half, the earlier footage was being played back at the same time, so Stevens was hearing himself say the lines to respond to.“Today’s kind of fun,” Stevens told me with a laugh, noting the really tricky sequence for him was one that he’d already shot the day before (but follows the coffin moments onscreen), where the two Davids go into a classroom and the Shadow King/Xavier history is explained.“Yesterday was very challenging,” Stevens remarked. “It was a whole day of blackboards - it was literally a whole day of two Davids. It’s essentially a very smart series recap, but it’s David kind of figuring out his s**t -- “What do we know?” -- and going through and plotting everything. This [in the coffin] is sort of the introduction of those two characters, which is kind of fun and it’s more contained. But yes, I’ve had this script for a couple of weeks now, just over two weeks probably, and it’s been weighing pretty heavily on me. All of these words, all of these ideas. I mean, what an amazing challenge! And every episode has been something that I’ve never done before, never even attempted before, and I know a lot of people have done these sort of double scenes with themselves, and they’ve always looked like fun. I’ve always wanted to try one. So yeah, it’s been nice to try that.”Midthunder in the meantime was working with the show’s stunt coordinator and several stuntmen, going through how Kerry would fight her attackers over and over again. As she told me afterwards, “It’s very complicated. But that’s sort of the fun challenge of the show. Action is one-dimensional. You see it. It’s punching and kicking and spinning and eventually that gets old. But in the show, everything is really layered that way so here you’re dealing with the fight but you’re dealing with multiple realities and multiple realities that everybody is jumping between.”In “Chapter 7,” not only was Kerry stuck in the Shadow King’s mental projection, but thanks to Cary and Syd, she was given a pair of glasses that helped her see through the illusion – when she could keep them on.As Midthunder put it, “For Kerry, she’s jumping between these realities and with these different mindsets and having to deal with who she is. She’s been disoriented for a while so to come out and step back into who she is, put that skin back on, and try to shake the place that she just was. She’s dealing with all that and having to take on a bunch of people and then having these two sort of realities… there’s a lot going on. So for me it’s a lot to process and think about and try to include but that’s the fun thing. It’s a challenge but it’s really fun. Then it’s a big team effort because we bring in Dennie [Gordon] the director and Dana Gonzales the DP. On the page it looks like ‘Kerry fights a bunch of people. Kerry fights nobody. Glasses are on, glasses are off.’ But you get everybody involved and it’s a big, elaborate thing [filled with] timing and tempo and thought and feeling.”While Legion has certainly taken its own path in regards to what the comic book set up, Stevens said he felt this storyline -- and seeing David speak with his own alternate personality -- had notable nods to the source material. As he put it, “In the comics, this is sort of the extent of what is inside David. We could do a hundred seasons of this show and not get to some of the really freaky stuff, like creatures - it’s not just humans that are in there, it’s all sorts of weird stuff going on. This is, I guess, relatively mildly!”As for the idea of using a British accent, Stevens revealed, “I checked in with Noah [Hawley] when he sent me that scene, and I was thinking of different ways of distinguishing [the two Davids], and I was like, ‘Well, it’s kind of a little nod to the Professor X thing,’ which we’ve kind of laced again through the series without getting too explicit. There are definitely rewards for people who know the comics. I don’t think at any point we’re directly adapting any story, or even any frame of a comic, but the paradigm exists. So this idea of characters being locked in there, of a battle for control over David and his powers, of this ongoing throughout history kind of thing... We use that and borrow that. But the British thing, I said to Noah, ‘Well, what about if we make him British?’ And he immediately was like, ‘Yeah, I guess deep down all of our rational selves are probably British.’ I was like, ‘Oh, good. That sounds like an endorsement, so I’ll go with that.’ I’m not sure how true that is, but anyway, it seemed funny to me!”

Eric Goldman is Executive Editor of IGN TV. You can follow him on Twitter at @TheEricGoldman , IGN at ericgoldman-ign and Facebook at Facebook.com/TheEricGoldman