Major Arrowverse Character Dies in "Crisis on Earth-X, Part 4"

Major spoilers ahead for "Crisis on Earth-X," tonight's CW/DC crossover event.

As producers have alluded to for months, a major character from one of The CW's four DC Universe shows died in the final part of this week's "Crisis on Earth-X" crossover.

Professor Martin Stein, one half of Firestorm and a veteran of the Arrowverse going all the way back to the first season of The Flash, was gunned down by Nazis on Earth-X while working to reactivate a gateway home and save the combined forces of Earth-1's superheroes.

The character, played by Victor Garber, has been a series regular on DC's Legends of Tomorrow since the series launched two years ago.

Initially, Garber was one half of Firestorm alongside Ronnie Raymond (Robbie Amell), after whom his recently-born grandson was named. After Legends of Tomorrow was greenlit, Amell could not commit to the series and was written out, replaced by Franz Drameh's Jax. Firestorm's powers only work when both halves are present, and if the pair are out of contact for too long, they will die.

Since the birth of his grandson, Stein has been talking about retirement, and in recent episodes, Jax and Ray Palmer have been working to separate the two without catastrophic results. Based on their research (and the research done to free Barry Allen from the Speed Force), Cisco recently discovered a way to separate Firestorm, but it would strip both halves of their powers.

It was that "cure" which actually killed Stein, when he took it so that his injuries would stop taking a toll on Jax, who has a physiological connection to the scientist. The loss of Stein played through the rest of the episode, taking quite a toll on

"Crisis on Earth-X" began last night at 8 p.m. ET/PT and runs for two hours beginning at 8 yesterday and today. Unless you have an easy way of getting caught up on your DVR, hang around and first thing in the morning you can buy digital copies on iTunes, Vudu, and other digital streaming services -- or watch it for free with ads on The CW's website or app.

The CW's DC superhero series will return with their midseason finales next week, beginning with Supergirl at 8 p.m. ET/PT and continuing with The Flash (Tuesday at 8), DC's Legends of Tomorrow (Tuesday at 9) and Arrow (Thursday at 9).