We've already learned that Grant Gustin will be making an appearance on Supergirl as The Flash.

Now we know just what he'll be doing there!

He'll arrive in National City suddenly, by way of an alternate universe. In exchange for help in finding his way home, The Flash will team up with Kara aka Supergirl, providing her with a new ally, to do battle against Siobhan, aka Silver Banshee, and Livewire.

Also guest starring in the March 28th episode titled "Worlds Finest" is Italia Ricci (Chasing Life) as Siobhan and Brit Morgan (True Blood) as Livewire.

They're doing this whole thing up really nice, and the full poster style promotion can be seen below.

Whether this solo-visit will open up the doors someday in the future for other Central City residents to visit National City or vice versa will probably depend upon the success of the initial outing.

I do know Supergirl is the more expensive show to produce, so it would be more likely to see another visit from Flash characters then for Supergirl to drop in on STAR Labs.

What do you think fans? Are you ready to see this happen? If you've never watched one or the other, will you be tuning in?

Let us know in the comments!

You can always catch up by watching Supergirl online right here via TV Fanatic. There's still time!

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Carissa Pavlica is the managing editor and a staff writer and critic for TV Fanatic. She's a member of the Critic's Choice Association, enjoys mentoring writers, conversing with cats, and passionately discussing the nuances of television and film with anyone who will listen. Follow her on X and email her here at TV Fanatic.