The Flash showrunner Eric Wallace says the inclusion of Cress Williams' Jefferson Pierce/Black Lightning and Javicia Leslie's Ryan Wilder/Batwoman was absolutely essential to making Season 8's five-episode "Armageddon" event a reality.

"But when I looked at what Barry [Allen]'s journey was, I realized there were two characters that had to be in the episode and I started there," Wallace said in an exclusive interview with CBR. "The story of 'Armageddon' cannot be told [without] Black Lightning and without Batwoman. They had to be in it. So that's really where we started, right? It turned out better than I even imagined, because now we have these wonderful scenes between Cress and Grant [Gustin], which we saw a little bit of in Season 6, that are taken to a whole new level."

RELATED: Batwoman Debuts First Photo of the Show's Killer New Poison Ivy

The showrunner continued, "Also, quite frankly, I wanted to see two powerful Black women in the Arrowverse meeting for the first time and interacting. So that meant, 'How would Iris West-Allen finally meet Ryan Wilder'" and I'm happy to say -- I won't tell you how, but not only is it just wonderful and their chemistry is incredible, but it's also funny... They're just terrific together. So that's where we started, because Batwoman and Black Lightning were integral to the story."

Williams starred as Jefferson Pierce throughout the entirety of Black Lightning, which aired on The CW -- home of the Arrowverse -- for four seasons from 2018 to 2021. While Black Lightning was initially a standalone series separate from the Arrowverse, it was officially integrated into The CW's shared DC television universe as a result of the "Crisis on Infinite Earths" crossover event, which aired from late 2019 to early 2020, coinciding with Black Lightning Season 3. The Flash's "Armageddon" event marks Williams' first time playing Black Lightning since the character's solo series came to an end earlier this year.

RELATED: The Flash: Armageddon Promo Leans Into Barry Allen As the Event's True Villain

Meanwhile, Leslie currently stars as Ryan Wilder on Batwoman, which premiered its third season on The CW last month. The original Batwoman, Kate Kane (played by Ruby Rose) originally debuted in the Arrowverse during the "Elseworlds" crossover event in 2018, with a Batwoman solo series following suit. Following Rose's now-controversial exit after Batwoman's first season, Leslie was tapped to star as Ryan, the new Batwoman, moving forward. Williams and Leslie are joined in the "Armageddon" event by Arrow alum Katherine McNamara, who reprises her role as Mia Queen.

"Armageddon, Part 1" premiered on Nov. 16 to kick off The Flash Season 8. The five-episode event will air weekly, concluding on Dec. 14. "A powerful alien threat arrives on Earth under mysterious circumstances and Barry, Iris and the rest of Team Flash are pushed to their limits in a desperate battle to save the world," the event's official synopsis reads. "But with time running out, and the fate of humanity at stake, Flash and his companions will also need to enlist the help of some old friends if the forces of good are to prevail."

The Flash airs Tuesdays at 8 p.m. ET on The CW.

KEEP READING: The Flash Boss Reveals Reverse-Flash's New Reason for Hating Barry Allen