The Vikings character drew sympathy from fans when he was introduced as Ragnar Lothbrok's crippled son in season four -- but took a turn after proving himself as a leader of the Great Heathen Army and driving an axe through the heart of his brother, Sigurd (David Lindström), in the season four finale.
ET caught up with Alex Hogh Andersen ahead of Wednesday's season five premiere, where he previewed Ivar's struggles -- but chuckled at questions about his character's motives.
"That's always the question. Is he really sorry?" he cracked, reflecting on Ivar's huge move. "He's in remorse, because he knows what follows. There's a massive cliff now between him and his brothers, but most of his [remorse] is about hating the fact that he lost control of himself."
"He's so driven by his emotions; that's really his weakness, in a way. He would have liked to be way more in control than what he was in that given situation, and that will be a major thing throughout the season," Andersen teased. "It's a big wound."
Ivar finds another big turning point as he's separated from Floki (Gustaf Skarsgard) in Wednesday's episode (watch the clip above), when the fan favorite character decides to head off on his own journey of self discovery. As Andersen explains, the goodbye hits Ivar hard.
"That was his last and probably only friend," he concedes. "Floki leaves the moment [Ivar] really needs him to guide him, to mentor him. When he leaves, Ivar is just left alone to himself, and that's not always good. He's fighting a lot of demons, and him being a demon himself too, sometimes."
Floki's journey to Iceland makes room for fresh blood in England -- and Jonathan Rhys Meyers' Bishop Heahmund, who tries to help Aethelwulf (Moe Dunford) defend his land from the Vikings. Audiences will come to love the ensuing battle between Heahmund and Ivar -- but in real life, Meyers and Andersen couldn't have better chemistry.
"Johnny is phenomenal. He's so intense," Andersen marveled. "He's really great, and his character is phenomenally written by Michael [Hirst]. We needed someone to square off with Ivar, somebody who is kind of his equal. [Heahmund] is just as extreme, just on the other side of religion, and they have a lot of similarities. So [although they are enemies] there's a strange mutual respect between them, because they understand each other."
"On one of the first days [Meyers and I] had together, we were sitting in the tent after shooting, and we had just nailed the scene, and I was like, 'Dude, we have great chemistry, man.' And he just looked at me the way Johnny does, and he was like, 'There's nothing called chemistry. It's called great actors,' completely deadpan," he laughed. "I'll take that any day, Johnny, thank you very much. But he was tremendous to work with...Every single scene we have together, people will be on the tip of their chairs to figure out what's going to happen."
In a word, Andersen described the upcoming season five as "epic" -- "It's such an over-used word, but this season is literally epic," he insisted -- declaring that both viewers and Ivar aren't going to want to sit this one out.
"[This season] is the biggest we've done, and I also believe it could be the best," he said, adding that his character's best move would be to stay in the background for a bit -- "but that's not Ivar."
"He can't do that!" Andersen confessed. "On top of all this, there's still the Great Heathen Army going on the whole mission of taking over England, and he doesn't want to sit on the bench for that one."
Vikings returns with a two-hour season five premiere on Wednesday, Nov. 29 at 9 p.m. ET/PT on History. Check back to ETonline after the premiere for more on Vikings -- and more of the big changes coming Ivar's way.