"Vikings" season 4 will revolve around the lives and dreams of Ragnar Lothbrok (Travis Fimmel), his ex-wife Lagertha (Katheryn Winnick) and their son Bjorn Ironside (Alexander Ludwig).

The show will return on History Channel with a time jump and focus on the various challenges faced by the Viking leader. Apart from his health problems, Fimmel's character will also have trust issues, teased Michael Hirst.

"For sure he's got some trust issues. It feels like everyone around him has betrayed him at some point. He doesn't trust anyone. He really feels alone in the world. He got very close to death, he's very intrigued by death and a lot of this year is his fascination with death like Odin. Odin hung himself to feel how it felt to be dead," Crossmap quoted him.

In the meantime, Ragnar's son Bjorn will struggle to earn the trust of his people and prove himself to be a good leader. According to Hirst, the character will end up doing something extraordinary in the first few episodes of "Vikings" season 4.

"It's a very important part of the season and that plays out over the first three or four episodes of the new season. It's a big storyline. We went to Canada to shoot some of it," he added.

On the other hand, Lagertha will return as a more powerful character in the upcoming sequel of the history drama series. "She has an amazing story arc this season; something so unexpected that I can't even begin to talk about it because I would immediately say too much. She will always be in the mix and she to me is Ragnar's equal in so many ways," Hirst told The Hollywood Reporter.

So fans of "Vikings" can expect major changes in the lives of their favourite characters when the show returns on History Channel with season 4 in 2016.