"Vikings" season 3 ended with a successful raid on Paris but it left Ragnar (Travis Fimmel) gravely wounded while his brother Rollo (Clive Standen) stayed to wed the daughter of Emperor Charles (Lothaire Bluteau). Meanwhile, season 4 may feature Ragnar's son Bjorn (Alexander Ludwig) waging wars at home and abroad. 

According to a report from Zap2It a while back, Ludwig stated that he had not yet read the whole script for season 4 but was able to state that his character Bjorn will retaliate against Rollo for his betrayal.

"He's so hurt and he's going to kill him. In his eyes, there're certain things you can't forgive," he said. 

A previous interview with series creator Michael Hirst from Variety also revealed that the fight between Rollo and Ragnar's family will grow to new heights in season 4 and will lead to dire consequences.

"But the conflict now is at a much higher level," Hirst stated, "but it has different sorts of ramifications too." 

Bjorn's problems don't just stop with Rollo, however. As previously reported, Bjorn will be set to succeed Ragnar as the leader of Kattegat and King of Denmark but he will still need to contend with his brothers for that title, particularly Ivar the Boneless. Ivar is the fourth son of Ragnar from his second wife Princess Aslaug (Alyssa Sutherland). 

All of Ragnar's sons have become legends in their own right, with some arguably more famous and successful than their father, and season 4 may see them beginning to carve their destinies as they branch out away from Ragnar and their home in Kattegat. However, as Bjorn is the oldest, season 4 may primarily focus on his adventures first. 

Ludwig stated as much during the "Vikings" Comic-Con panel where he explained that season 4 will see Bjorn stepping up and becoming his own man, running things while his father cannot. 

"Vikings" season 4 will premiere in 2016.