An ally's return will be a big boost to Clarke (Eliza Taylor), who has been worrying about the looming nuclear disaster in the upcoming season of "The 100."

It has been previously revealed that Roan (Zach McGowan) is alive. As per reports, McGowan has been promoted to a series regular. The actor also posted the good news on his Twitter account.

The last time viewers saw Roan, he was shot by Kane (Henry Ian Cusick). The Grounders then dragged him away and it looked like he was finished for good. As the King of the Ice Nation, Roan has been a huge help to Clarke, especially when she was trying to negotiate a truce between his kingdom and Arkadia. The two struck an alliance and Clarke was saddened when she heard the news that he might have passed away.

The future is dire for the survivors, as ALIE's (Erica Cerra) prediction is coming true. Humanity will be wiped out after the nuclear disaster.

Showrunner Jason Rothenberg has previously said there is no stopping it. In Clarke's point of view, everyone must be saved or else, they are doomed. Surviving the apocalypse, however, is no easy task. All of them must come up with a plan. Roan will be a great help for Clarke in this one, since they trust each other.

"First they have to make sure it's the truth - that I established today that it is the truth. Then they have to decide how, and whether they can stop it. And ultimately they realize they can't. And then it's about how do we survive? And it's about figuring out the various options. They have to save more than just themselves. They have to save everybody, otherwise they fail. At least that's the way Clarke looks at it," the EP said.

"The 100" season 4 is expected to air late 2016 or early 2017 on the CW.