CBS' Supergirl aired its 15th episode last night, Solitude, which gave us our first look at the Fortress of Solitude occupied by Kara's (Melissa Benoist) cousin, Superman. We had previously seen a sneak peek at this iconic location before the episode aired, but for those who tuned in last night, there was a special Easter Egg. One of the items many fans noticed in the Fortress was a Legion Flight ring, which you can see below in a photo from Entertainment Weekly writer Natalie Abrams.

The episode centered on Kara Zor-El and Jimmy Olsen (Mehcad Brooks) visiting the Fortress of Solitude, in search of a way to defeat Supergirl's new nemesis, Indigo, played by Laura Vandervoort. Much like the early Superman movies, this Fortress appeared to be made of ice crystals and featured a nod to the Kryptonian Museum in the comics, with statues of Jor-El and Lara, along with a hidden door opened by a key that only Kryptonians are strong enough to lift. Among Kal-El's other artifacts on display was a Legion Flight ring, which could tease that the Legion of Superheroes is coming to the show.

In the DC Comics, the Legion of Superheroes story was set in the 30th Century, following a team of super-powered young adults. The group was created by Cosmic Boy, Lightning Lad and Saturn Girl, and was funded by billionaire R.J. Brande, whose life the heroes once saved. Cosmic Boy has the ability to manipulate metal objects with his super-magnetism, while Saturn Girl can summon people from anywhere in the world, along with the ability to control the weak-minded. Lightning Lad can shoot bolts of lightning from his body.

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DC's Geoff Johns has teased in the past that the Legion would be featured in the sprawling TV universe, which may culminate with Supergirl's upcoming crossover with The CW's The Flash, airing on March 28. In an episode of The Flash from earlier this month, Welcome to Earth-2, Supergirl was spotted, along with several other heroes, while Barry Allen was journeying to Earth-2. Some eagle-eyed fans noticed that there was also a Legion Flight ring that was shown in the speed force.

As of now, no plot details have been released for the Supergirl/The Flash crossover, but it's certainly possible that the Legion of Superheroes could play into this episode, since we've seen these Legion Flight rings on both shows. Take a look at the photo of this Legion Flight ring from last night's Supergirl, plus photos from Welcome to Earth-2 that feature both Kara and the ring. Do you think we'll learn more about this Legion of Superheroes tie-in during the crossover episode?