Just days after we first learned that The Flash would race over to Supergirl by March’s end, The CW teased their first official crossover with a vision of Kara in Barry’s “Welcome to Earth-2.” Eagle-eyed viewers also spotted a Legion of Super-Heroes easter egg as well, which tonight’s Supergirl revealed as another connection between the two worlds. What could it mean?

You’re warned of both Supergirl spoilers through Monday’s “Solitude,” as well as The Flash‘s Earth-2 arc, but where previously DC boss Geoff Johns had teased that the 31st century “Legion of Super-Heroes” would get a shout-out on an upcoming series, most presumed that the Legion flight ring in Barry’s journey to Earth-2 marked the extent of it:

The CW

Not so, apparently, as Supergirl’s trip to Superman’s Fortress of “Solitude” revealed the ring in question as one of Kal-El’s many relics adorning the arctic getaway, perhaps indicating that he’d met the futuristic team before.

Thus far, almost everything observed in the “Welcome to Earth-2” breach has had some bearing on future Arrow-verse events (with the exception of John Wesley Shipp’s Flash), including Barry’s upcoming trip to National City, as well as the Legends of Tomorrow arrivals of Jonah Hex and Connor Hawke. It’s clear in this case at least that The CW simply borrowed Supergirl footage for the reference, but why make a habit of emphasizing the ring on both shows?

Could the Legion somehow factor into the crossover teamup against Silver Banshee and Livewire, or might Barry himself visit the Fortress of Solitude during the “Worlds Finest” event? Could Warner Bros. be gauging interest in a Legion series, or just tossing out easter eggs for fans?

At the very least, we also know that while “Worlds Finest” airs on March 28, the prior week’s Flash outing “Flash Back” episode will see Barry again traveling through time, which could well end with him somehow breaching dimensions to Kara’s National City.

In the meantime, stay tuned for the latest on The Flash and Supergirl crossover, and get to speculatin’ on some theories!

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