Ragnar Lothbrok's (Travis Fimmel) life is in further danger in the next episode of "Vikings" season 4.

In one of the sneak peeks at episode 4, titled "Yol," King Aelle of Northumbria (Ivan Kaye) returns to Wessex, saying that he will kill the King of Denmark.

According to historical facts, Aelle was the once responsible for the death of the mighty Norse leader by throwing him in a pit filled with venomous snakes. But this ignited the 14-year English invasion after Ragnar's sons found out about their father's death.

But in the historical drama series, little is known about Aelle's reasons why he wants to kill Ragnar. But he seems unpleased with how his family relations are developing in the upcoming episode of season 4.

Meanwhile, another sneak peek shows Ragnar interrogating his wife Aslaug's (Alyssa Sutherland) new slave named Yidu (Dianne Doan).

In the video, Ragnar forces Yidu to tell him how she ended up being a slave.

"I was sailing with members of my family. Pirates came aboard and slaughtered some of us, and others they kept as they sailed. They separated me from my brothers," Yidu says. She could not finish her statement, so Ragnar asks her if they raped her. She says that the pirates did not dare rape her but mentions that they dragged her on a long journey before selling her to the people in Paris.

In an exclusive interview with Design & Trend, Doan talked about her character and where she and Ragnar will end up in the upcoming season.

According to the actress, Ragnar seems drawn to Yidu because of her appearance and ethnic background. "The relationship stems from Ragnar's curiosity of her past, where she comes from, who rules it and what her thoughts are about religion and death," Doan said.

The episode will also show the growing tension between Ragnar and Aslaug, as well as the fate of Rollo in Paris.

"Vikings" season 4 episode 4 airs Thursday, March 10, on History Channel.