There have been rumors but it's been confirmed that The Flash/Barry Allen will be making an appearance on Supergirl. Everyone kind of expected this since they are produced by the same company and though they air on different TV stations The Flash on CW and Supergirl on CBS, those two networks are owned by the same company. I think it's a great idea doing a crossover. Hopefully it will get more people to watch Supergirl and vice versa with The Flash. What's great is that this also means Arrow and Legends of Tomorrow are also in this larger universe. Of course with the Flash able to move between Earths (Multiverse) Supergirl might be in a different verse so she may never crossover with the others. Guess will just have to wait and see when the episode airs.. which is suppose to happen on March 28th. Can't wait to see these two superheros come face to face.