when does the flash show up in supergirl
Supergirl (TV series) On February 3, 2016, it was announced that Grant Gustin, who appears as Barry Allen / Flash on The Flash, would appear in the eighteenth episode of the first season, "Worlds Finest".[113] While no plot details on the episodes were released at the time, Ross A. Lincoln of Deadline.com noted that "the in-universe reason" for the crossover was due to Barry's ability to travel to various dimensions, thus implying that Supergirl exists on an alternate Earth to the Arrowverse in a multiverse.[114] The Flash episode "Welcome to Earth-2" confirmed this, showing an image of Benoist as Supergirl during a sequence where characters travel through that multiverse.[115] The earth that the series inhabits is Earth-38 in the Arrowverse multiverse,[116] and has been informally referred to as "Earth-CBS" by Marc Guggenheim, one of the creators of Arrow.[117]
The Flash (season 4) The fourth season is set to begin airing on October 10, 2017, on The CW.