Ragnar's men better watch their backs; two new Viking characters will make their season 4 debut in such away that both the Norsemen and the audience will have their jaws on the floor.

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Vikings Clive Standen (Rollo) journeyed to Australia's Oz Comic-Con in September, and while he was there, the actor dished on at least one shocking development fans should prepare for in season 4.

"We've got some new characters. We've got Halfdan the Black and Harald Finehair, two new Viking characters who are deadly and quite tricksy," Standen teased, according to The AU Review. "I can't really say much about them because they come in and they explode on the screen in a certain way that some of the more regular Vikings that the audience have got to know are going to be shocked."

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Brothers, the characters of Halfdan (Jasper Paakkonen) and King Harald Finehair (Peter Franzen) were added to the cast back in May. Their springtime announcement indicates that they will feature in season 4's opening episodes, but their motives currently remain unclear.

It sounds like fans will have to wait until 2016 to find out just what shocking plans Halfdan and Finehair have planned for the cast of History Channel's Vikings.