Vikings season 4 featured a shocking twist in episode 5 titled Promised, which aired on 17 March. Lagertha's shocking act in the final scenes of the episode caused a major character's death.
She emerged as one of the best characters in the series after she finally took revenge from the Viking warrior Kalf. In the episode, the shieldmaiden revealed that she was pregnant and Kalf immediately proposed to marry her. But just before the wedding she stabbed him to death and reclaimed Earldom.
"Kalf's destiny was very much defined by his actions. When he did usurp Lagertha, there were consequences. I think Michael Hirst wrote an incredible arc for Kalf. He was subservient and loyal to Lagerta. It was fun to play a sort of naive kid who's not looked to be a threat in any way, to come into power and prove himself in Paris," actor Ben Robson, who plays Kalf in the searies, told EW.
The love-hate relationship between the couple goes back to episode one of the current season, where Kalf announced that he and Lagertha would share Earldom, though Ragnar's former wife knew that she deserved the throne all for herself.
She also told him casually that one day she would kill him. However, Kalf choose to ignore the threat and instead tried to kill her son Bjorn in the wilderness.
"I don't think it's a case of him not taking it seriously, but I think it was a case of not really believing it would happen. I think he underestimated the betrayal of what he did. He felt that they found a level playing ground to carry on forward with," said Robson.
Episode 6 of Vikings season 4 titled What Might Have Been will air on 24 March on History Channel.