In the season three finale, Cain lured Lucifer and Chloe into a trap and tried to kill them both.

Believing Cain had killed Chloe, in a fit of rage Lucifer killed Cain, stabbing him to death with one of Mazes (Lesley Ann-Brandt) demon blades.

Cain originally believed he would be going to heaven, confessing he has no regrets.

However, Lucifer knew Cain regretted killing Charlotte and as a result he will torture himself with guilt in hell for eternity, alongisde his brother.

As Lucifer returned to Hell at the end of season four, a Cain and Lucifer reunion could well be on the cards.

Unfortunately, Welling has not confirmed whether he would reprise his role as Cain in the fifth series.

Welling is currently starring in the Arrowverse crossover Crisis on Infinite Earths as Clark Kent/Superman from Smallville.

Excerpt from:
Lucifer recap: What happened to Cain and Abel? Will they return for season 5? - Express