'Vikings' season 4 episode 15 spoilers: Ragnar and Ivar plot against enemies; Aslaug to reappear in dream sequence?

Ragnar (Travis Fimmel) becomes closer to his son Ivar (Alex Høgh Andersen) on the upcoming episode of History's hit drama "Vikings" season 4.

Titled "All His Angels," this week's episode will see Ragnar bond with Ivar as they plan to strike the enemies. To give viewers an idea of what's to come, the official synopsis reads: "Ragnar and Ivar plot against the Saxons and reach a new level of understanding."

According to spoiler reports, Ivar will finally get the time and attention he longed from his father. It is speculated that Ragnar will be killed by King Aelle (Ivan Kaye) soon, and his sons will avenge his death. If the show keeps true to the history books, Ivar will serve as the heir to his father's throne.

Last week, viewers said goodbye to Queen Aslaug (Alyssa Sutherland) after her unexpected death at the hands of Ragnar's first love, Lagertha (Katheryn Winnick). After losing her husband Ragnar to the princess Aslaug back in season 2, Lagertha has spent years planning her next move to become a female leader in the Viking world.

Wednesday's episode saw Lagertha make her biggest move yet when she came back to Kattegat while Ragnar is away. Upon arriving at the area, she shot Aslaug in the back with an arrow, despite the queen's attempts to bargain her way to safe passage.

Speaking with The Hollywood Reporter, Sutherland mentioned that she was ready for Aslaug's death even before her character's fate was revealed to her last year. She also shared her thoughts on a possible return through a vision or dream sequence. "If that were to happen, it would be a very quick scene," she said. "And to me it would have to be Ivar that she would have to appear before. That's up to Michael, but the door is always open like that on 'Vikings.' I was ready for Aslaug to be done," she added.

The fourth season of "Vikings" airs every Wednesday night at 9 p.m. ET on History.