Although the two shows are on different networks (The CW for Flash, CBS for Supergirl), both shows are executive produced by Greg Berlanti and Andrew Kreisberg, who explained, “We are so incredibly excited to announce something that we have dreamed of happening since we starting making Supergirl. We want to thank Grant Gustin for making the time to come visit (on top of his already immense workload) and all of the folks at CBS, The CW, Warner Bros. and DC for working this out. And finally thanks to the fans and journalists who have kept asking for this to happen. It is our pleasure and hope to create an episode worthy of everyone’s enthusiasm and support.”
Unlike many crossovers – such as the recent Bones/Sleepy Hollow event – the story won’t start on one show and conclude on another: likely for budgetary reasons, this is a one-way trip for Gustin; at present there are no plans for Melissa Benoist to play Kara/Supergirl over on The Flash (or Arrow or Legends of Tomorrow…)
Because the run of episodes in the US is sporadic at present, Sky has yet to pick up from episode 9; it is believed that they will start again on 1 April, in which case the crossover episode will air in mid to late May.