Rollo and Bjorn will collaborate in the second half of "Vikings" season 4.

The next installment of the series will see a surprising collaboration between the two characters as they cross the Mediterranean Sea. Also, it will reveal the identity of the character who was spotted kissing Lagertha in the previous installment.

Recently, the promo video for "Vikings" midseason 4 was unveiled at the San Diego Comic-Con 2016, and fans can't wait for its premiere.  Despite lack of official details as to when the series will return, some speculate that it will return when "Game of Thrones" comes to an end.

In the promo video for the series, Rollo is shown unwillingly helping Bjorn as he traverses the Mediterranean Sea. It can be recalled that Rollo already abandoned his Vikings roots to become part of the Parisian community. He also defeated Ragnar through the help of the French army.

The turn of events seems to divide fans, since some sympathize with Rollo while some abhor him, believing that his actions are mostly triggered by his hate and jealousy.

The trailer released at the Comic-Con also revealed another woman kissing Lagartha inside the bedroom. In the previous installment, Legertha was also spotted in a three-some, and even kissed Kwenthrith.

The promo video further revealed that the midseason will put the army of Lagertha in the spotlight. Fans have yet to know what special role she and her new lover will play in the new series.

As for Ragnar, spoilers suggest that he will die since Travis Fimmel has signed up for "Warcraft."

"Vikings" season 4 is expected to return this fall.