The Season 4 of "Vikings" is set to premiere in 2016, and as early as now, various possible storylines have been discussed over the Internet by fans and even the showrunner themselves. Recent reports state that Aslaug may not easily give up her power as Queen of Denmark, a position which she took in Ragnar's absence in the previous season. Other reports also claim that Ragnar's sons, Bjorn and Ivar, will go head to head as they fight for the throne as Ragnar's heir.
According to Day Herald, Ragnar (Travis Fimmel) will face a lot of difficulties in "Vikings" Season 4. Apart from his brother Rollo's (Clive Standen) betrayal and his terminal injury from the battle of Paris, he will also reportedly face a difficult situation with his wife Aslaug (Alyssa Sutherland).
As previously mentioned, Aslaug reigned as the Queen of Denmark in Ragnar's absence in the previous season, and speculations suggest that when Ragnar comes back, Aslaug won't easily let go of the power she enjoyed while her husband was away.
It was said that she will be reluctant to fade in the shadow of her husband once again, and it was previously reported that she may plot to take over the kingdom. Showrunner Michael Hirst also apparently previously hinted that Aslaug will be an important character in Season 4.
Meanwhile, it has been widely speculated that Ragnar will have to be replaced by his rightful heir due to his injury and imminent death. According to reports, Ragnar's eldest son Bjorn (Alexander Ludwig) will take over the throne, but Ragnar's other son, Ivar, whose adult version is yet to be cast in the show, will oppose the idea along with several other people. The brothers will reportedly clash and fight over the throne.
"Vikings" Season 4 has been confirmed to return to History channel next year. However, no specific release date has been specified.