Wentworth Miller as Citizen Cold
Leo Snart (Wentworth Miller), aka Citizen Cold, helps Barry (Grant Gustin) and his team transport dangerous metahuman Fallout (Ryan Alexander McDonald) in Season 4, episode 19 of CW’s “The Flash.” The CW

Leo Snart, aka Citizen Cold, returns to Earth-1 in next week’s episode of “The Flash.”

According to the synopsis for Season 4, episode 19 of the CW series, Barry (Grant Gustin) calls Leo (Wentworth Miller) for help when Team Flash needs to transport a dangerous meta.

The trailer for the installment reveals that the meta the team needs to move to another location is Fallout (Ryan Alexander McDonald). Also known as Neil Borman, Fallout first appeared in Season 4, episode 10, in which he unknowingly gave people around him radiation sickness. Because he was about to go nuclear, Caitlin/Killer Frost (Danielle Panabaker) tried to cool him down by hitting him with a layer of ice. But when it failed, Barry ran circles around Fallout to create a vacuum, and at Harry’s (Tom Cavanagh) suggestion, Cisco (Carlos Valdes) opened a breach, sending Fallout’s nuclear blast to Earth-15.

In the trailer for the next episode, Leo agrees to help Team Flash, but he only has 24 hours to get the job done.

The episode appears to be the final Arrowverse appearance of Miller, who announced his imminent departure from The CW’s DC TV universe last November.

Although Miller’s Arrowverse stint is coming to an end, Gustin is hoping that Miller will return to “The Flash” at some point in the future. “I hope he comes back,” Gustin told ComicBook.com and other reporters last November when asked about Miller’s exit. “Because I remember when it was like, they killed off Wentworth a while back when he was a Legend, and then he was back and I worked with him a couple times. So I’ll just keep my fingers crossed that I get to work with him again.”

“The fans love those two characters together,” Gustin said of Barry and Miller’s original Arrowverse character, Captain Cold.“We always talk about [that] when we act together. We’re like, ‘Man, I love these scenes.’ They’re different than anything else that the two of us do together on our show. There’s all kinds of dynamics there. They started as enemies, and they came to respect each other and I think they came to care about each other even. But there’s trust issues there, probably on both sides. There’s a lot going on. There’s probably more going on with that relationship than almost any other Barry relationship.”

“The Flash” Season 4, episode 19, titled “Fury Rogue,” airs on Tuesday, April 24 at 8 p.m. EDT on The CW.