Could the Legion of Super-Heroes, long expected to become a major part of the story on Supergirl, finally be making its way to The CW...by way of a crossover event with the network's other superheroes? This year's "Arrowverse crossover" won't be airing for another few months, with the first part of the two-night event airing on November 27, but that doesn't mean the shows aren't already in pre-production. So far, it's been relatively quiet as to what will factor in to the content of said crossover, although the wedding of The Flash's Barry Allen and Iris West is one of the more popular guesses. Fueling the fires of speculation is Arrow and DC's Legends of Tomorrow Executive Producer Marc Guggenheim who has shared a few pieces of pre-production work on his Twitter feed, leading us to a big but very strong possibility: What if this year's super-crossover involves the Legion of Super-Heroes? After all, how else could you top an alien invasion? Below, find some clues and other reasons to support this theory.

The Legion Clubhouse? Last year's Arrowverse crossover offered their own nod to the classic Superfriends cartoon by shaping a STAR Labs facility to look like the Hall of Justice. This item that is currently being sculpted for the crossover looks almost like a futuristic standing fortress, and if we're not mistaken, that could very well be an "L." The Legion Clubhouse first appeared in DC Comics way back in 1958's Adventure Comics #247, coincidentally the first comic book to ever feature the team. In one story that may not be a part of official continuity the Clubhouse was actually once a person named "Fortress Lad" who sacrificed himself to protect the Legion. (Photo: Marc Guggenheim/Twitter)

A Mask The easy guess would be that this is a reference to the Golden Age Sandman or his protege, Sand, from the late-century JSA comic books. There's one thing wrong with the Sandman theory, at least: There already is a Sandman gas mask on the Waverider set for Legends of Tomorrow, so they wouldn't need to build one. Aviator type goggles might also point to a character like Enemy Ace, but what if this piece that is being built is actually a helmet? More specifically, the helmet of either Ferro Lad (who might look a bit too much like Iron Man if they took his live action look directly from the comics) or Legion villain the Persuader (who himself appeared in the Legion's Smallville appearance?) Created by future Marvel and Valiant icon Jim Shooter when he was a teenager, Ferro Lad (Andrew Nolan) was the first Legionnaire to die. The atomic axe-wielding Persuader was also created by Shooter as a member of the "Fatal Five." (Photo: Marc Guggenheim/Twitter)

Legacy Assuming that the crossover does indeed feature the wedding of Barry Allen and Iris West, what better way to have them rocked by the future than to meet their granddaughter? Jenni Ognats a.k.a. XS is speedster and member of the Legion of Super-Heroes, and she also happens to be the daughter of Dawn Allen, one of the "Tornado Twins" and child of Barry and Iris in the future. A chance to meet their grandchild could be an inspiring sign to go through with the wedding, and a good counterpoint to the threats that usually come from later years in the timeline. If Jenni Ognats is not a possibility, the Allens' other grandchild, the impulsive Bart, is quite popular and also originates from a future timeline in the comics. (Photo: DC Entertainment)

Mon-El Moving on over to Supergirl now, we saw in the Season 2 finale of the series that Mon-El has gone off into parts unknown, and we also know the comic book origin of Mon-El, in which he goes into the Phantom Zone and comes out a thousand years later as a major part of the Legion. What if the anxiously-awaited-by-many reunion between Kara and Mon-El plays out in that way, and he's got a new group of Super-friends in the future? And what if he wants her to stay there with him? That could add to new conflict, and it could explain Supergirl's role in the crossover, as well as why the Danvers sisters were called the story's core. Win-win.