'Vikings' season 4 spoilers: How Lagertha's new romance began and her hatred towards Aslaug deepened

"Vikings" season 4 has a lot in store for Lagertha (Katheryn Winnick), who not only comes back from the pits that Aslaug (Alyssa Sunderland) put her in, but with vengeance and a new partner.

Show creator Michael Hirst has already said that Lagertha is too important of a character to kill off, calling her the "soul" of the show. The latter half of the season will be big on the shieldmaiden.

First off, Lagertha will return and settle the score with Aslaug, who, in the midseason finale left her in a situation so helpless that many thought the character met her end.

Aslaug has somewhat become the ruler of Kattegat during Ragnar's (Travis Fimmel) absence. To Lagertha, she is nowhere near an effective ruler and has developed intense hatred toward her, which the revenge-motivated shieldmaiden will act upon in "Vikings" season 4.

However, she won't do it alone as she will be accompanied by her new partner Astrid (to be played by Josefin Asplund), who she feels very restful with and trustworthy.

"She's become a part of Lagertha's life. They are in a relationship," Hirst revealed to Entertainment Weekly, adding that it would not be much of a shock considering the kind of men Lagertha had in her life and the fact that she is "not that kind of a woman" to live alone.

"The point is, she's in a relationship with someone she feels more comfortable with, someone she feels she might be able to trust, and it's a woman," Hirst added.

In addition to that, Lagertha knows that she has responsibilities and ambitions, and "if she can help it, she's not gonna get involved with another guy who's gonna want immediately to take her earldom away from her."

Astrid won't do that, at least "not initially," as Hirst teased. Describing the "Vikings" season 4 newcomer, he said Asplund's character is a "breath of fresh air into the show" and is also "more modern."

"Vikings" season 4 will premiere this fall on History.