(WARNING: Spoilers for the Vikings Season 4 finale beyond this point. Read at your own risk!)

Unsurprisingly, the Vikings' finale had its fair share of victories and heartbreak.

After successfully winning the battle in Wessex — and losing poor Helga in the process — Ragnar's sons had to decide what to do next. Bjorn (Alexander Ludwig) announced he wanted to return to the Mediterranean. Ivar (Alex Høgh Anderson) wanted to lead warriors on raids to new lands. Hvitserk (Marco Islø), Ubbe (Jordan Patrick Smith) and Sigurd (David Lindström) wanted to stay in Wessex to establish and defend the farming community Ragnar always wanted.

When the brothers' began debating whether they should split up, the argument soon devolved to Sigurd and Ivar trading unforgivable insults until the latter was finally pushed to his edge. Without thinking, Ivar grabbed a nearby ax and flung it straight into his brother's chest, killing him within minutes.

Vikings creator Michael Hirst spoke with TVGuide.com about the consequences of Ivar's shocking action and what else to expect in Season 5.

There was already growing tension between Ragnar's sons after their victory in Wessex, so how will Ivar murdering Sigurd affect the remaining brothers' already fragile relationship?
Michael Hirst:
I think that obviously it will impact all the brothers. And I think you got the sense that they were only drawn together because of the one thing they had to do, which is to avenge the death of their father, which was, in Viking times, inescapable — especially because Ragnar had been so famous. And so the sons had to gather together to do that, but there were already strains in the relationships because of different mothers and everything. I think it's fairly obvious that the death of Sigurd by Ivar will usher in a time of great conflict between the brothers. And that conflict between brothers will end up in a world war.

Do you see Ivar's murder of Sigurd as a turning point in the character?
Hirst:
No, I think it's part of his character because if you remember when he was younger he killed another boy when they were playing a game. His mother Aslaug forgave him. He has always been an extreme character. He has brittle bone disease and we investigated that condition and we talked to people who had it and who had relatives who had it. And one of the things that it does is to make people very angry, of course. They can wake up one day and just break a bone by just doing something very simple. So they're used to being very angry a lot of the time. So whatever terrible things Ivar does, you can somehow just about forgive him because you know where he's come from and the struggles that he's gone through and the terrible pain and suffering that he's gone through. So I don't think Ivar killing Sigurd is defining because I think he's already done that, but it is a marker. It marks that there's nothing that will ever stop Ivar doing what he wants to do. He has no moral compass. He's not controlled by ethics or normal human considerations. For me, as a writer, that's amazing. I've just got a character on my hands who just can do anything and actually does proceed to do anything. But you do understand where that comes from. Of course, Sigurd is taunting him. And Ivar is very, very sensitive. He's a very sensitive guy.

Vikings star explains Ivar's cruel streak and rise to greatness

Does Ivar regret killing Sigurd at all?
Hirst:
He's completely divided. As I recall, in the first scene of Season 5 when they bury Sigurd, Ivar is weeping and saying it wasn't his fault, that Sigurd had pushed him, that he loved him, he was his brother. He didn't know why he did it. He had just made him angry. And I think you'll find that all the way through the history of Ivar is that he does terrible things and then he feels awful afterwards. He regrets doing these things. He can't help himself. It makes him an astonishingly interesting character to write. He doesn't think about the consequences. He does what he does and then he thinks about the consequences.

Ecbert (Linus Roache) wasn't the king when he signed the land over to the Vikings. What sort of repercussions from that will we see in Season 5?
Hirst:
Huge repercussions. Huge for his son and his grandchildren and everything. There's a lot that plays out as a result of Ecbert's decision. For me, personally, Ecbert was a huge character for me — just about as big as Ragnar. And the death of Ecbert was very difficult for me. I thought Linus was just unbelievable — absolutely unbelievable as a character and as a man at playing this conflicted, wonderful, weak, strong, poetic, brilliant king. I love him so much and I miss him.

We finally got our first look at Jonathan Rhys Meyers as Bishop Heahmund, who will become an antagonist to Ivar next season. What can you tease about his role going forward?
Hirst:
I knew that I needed a new Saxon character who might be able to stand up to the Vikings and I discovered these people called warrior bishops. They're real people and Heahmund was a real [person] and he was a precursor of the Knights of Templar. That's to say he was a young man of God. He was trained in the church. He was very devout and definitely a churchman, a spiritual person. But he was also a warrior. And so when it came to fighting, like the Knights of Templar did, they'd fight. And the thing about Heahmund that's interesting is he's kind of divided. He was prone to passion. Despite his very deep, devout religious belief, he was a passionate man who took advantage of women who looked up to him as a bishop and then he'd punish himself for his sins. He's a kind of Michael Hirst character, I have to say. He's a complex character. He punishes himself for his sins and yet he's a very brave, courageous and interesting person. And I just needed a Christian soldier who could stand up to Ivar because I knew that Ivar would just absolutely begin to dominate the great army. And so I needed someone. And Johnny was suggested to me as a possible player of Bishop Heahmund .... And so that seemed a good match to me because Johnny is compulsively watchful. Johnny is absolutely charismatic and that's what I needed. Because I think we found in Alex Hogh Andersen someone else who's very charismatic. And so I needed someone equally charismatic who could stand up to him or make a relationship with him, which he does.

Lagertha (Katheryn Winnick) finally took back Kattegatt, so now what is her driving motivation going into next season?
Hirst:
Having become queen - and this is very important to me actually, because Lagertha's actually one of the big, big characters in this show and I really love writing about her - so I thought Lagertha's going to try and rule as an intelligent woman, not as a man. So as we move forward into Season 5, she's faced with very difficult and compromising and strategic decisions about how to be a ruler and how to rule in the Viking world. And I think the decisions she makes are very intelligent and very interesting, but they come into conflict a lot with the male attitude towards ruling. She just doesn't rule like a man. She makes much more subtle, nuanced decisions. I wish I could tell you what they are, but I cant. But she does reinvent the role of ruler and she does absolutely reinvent the role of the queen in Viking society.

Floki (Gustaf Skarsgard) lost so much over the course of the season. How will he be different when the show returns?
Hirst:
Floki is like a man who's died except he hasn't died. He recognizes that he's lost everything that he's most cared for. He's lost his daughter. He's lost his friend Ragnar. And he's lost his wife. For him, his previous life is over. He's going to submit himself to the gods. He's going to get into a boat and he's going to sail away at the mercy of the tides and the mercy of the gods. He just feels he has to change his life completely. The end of the season is marked with huge change in Floki's life. But for all the fans, everyone who loves Floki as I do, don't worry. He's going to be around. He's going to do some pretty spectacular things in his new life.

We only briefly saw the Mediterranean this season. Now that Bjorn is going back, will we get to spend more time there and with Bjorn's journey?
Hirst:
Sure. Absolutely. Bjorn comes back to lead the great army against the killers of his father, but as he said at the end of the season, he wants to go back to the Mediterranean. And he goes back to the Mediterranean and boy, does that pay off. We shot scenes in Morocco that you won't believe.

Season 5 will be the first season without Ragnar in it at all. How did that change the way you approached the season, if at all?
Hirst:
It doesn't, because I never thought of it as Ragnar's show. This is Ragnar and his sons... and Ragnar never dies because he lives on through his sons. But also in terms of the show, the episode after Ragnar died, the audience went up. And the episode after that, the audience went up again. It's different around the world, but in America, more people have watched it since Ragnar's death. And that says something about why people watch the show. They're watching the show, but they're not watching individual actors.

Vikings will return for Season 5 later this year.