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when does the flash show up in supergirl
Worlds Finest, the eighteenth episode in the first season of the CBS television series Supergirl, features an appearance by The Flash
when does the flash reveal his identity in the eighteenth episode of supergirl
The speedster introduces himself as Barry Allen, a.k.a. the Flash, after Kara reveals herself as Supergirl in the 18th episode of season 1 of Supergirl

Question: did cat know the identity of the superhero
Self-contained rewrite: did cat know the flash's identity in the 18th episode of supergirl