Basically, Vikings Season 4 is going to take over where season three left off and that means that people are moving on from Athelstan’s death. The fans of the show were shocked with the death and it also hit Ragnar just as hard.
The addition of Yidu will be a major story line in the upcoming season since Althelstan’s death. Yidu will play a specific role for Ragnar in replacing the recently deceased. As for the other characters in the show, season four will be an extension of what they have been up to at this point.
Lagertha will continue to stand alone in the world of Vikings and she is also given the chance to show her strength each time she meets a new manly character. Vikings Season 4 is set to start on the 18th of February and will run for twenty episodes.