when does the flash cross over with arrow
Crisis on Earth-X "Crisis on Earth-X" is the fourth annual Arrowverse crossover event, featuring episodes of the live-action television series Supergirl, Arrow, The Flash, and Legends of Tomorrow on The CW. The crossover began on November 27, 2017, with Supergirl and Arrow, and concluded on November 28, with The Flash and Legends of Tomorrow. In "Crisis on Earth-X", Barry Allen and Iris West's friends come to Central City for their wedding, only to be interrupted when villains from Earth-X disrupt the proceedings.