This recap contains spoilers for the “Vikings” midseason finale, Season 4, Episode 10, titled “The Last Ship.”

After three seasons of simmering jealousy, Ragnar Lothbrok’s (Travis Fimmel) rivalry with his brother Rollo (Clive Standen) finally came to a head in a brutal battle in the April 21 epiode — but the long-awaited clash had an unexpected result, with Rollo and his Frankish forces defeating Ragnar and his Viking warriors. The episode then jumped forward several years, revealing that Ragnar left Kattegat after his loss, leaving his sons — Bjorn (Alexander Ludwig), Ivar (Alex Høgh Andersen), Ubbe (Jordan Patrick Smith), Hvitserk (Marco Ilsø) and Sigurd (David Lindstron) to grow up without their father, curious about his fate and (in some cases) resentful of his absence.

Variety spoke to “Vikings” creator Michael Hirst about the events of the midseason finale, the introduction of Ragnar’s adult sons and what’s ahead in the back half of Season 4. This interview has been lightly edited and condensed for clarity.

Why did now feel like the right time for Ragnar and Rollo’s confrontation, and why was it important for Rollo to win?

It was always going to happen. Rollo had rebelled before, when he tried to creep out from under Ragnar’s shadow — the Viking idea is that fame is everything, to be remembered for things, and he just felt that he was never going to be remembered. And then the Seer had told him that if he went to Paris that something extraordinary would happen. And I remember telling Clive that, and Clive was very excited by the idea, because Clive had thought himself that his character was always put upon and always beaten. But I said, “if you look at history, history tells you something different; the character you’re playing becomes one of the most impressive people in Dark Ages Frankia and establishes an empire, basically,” so I’m only following history. Whatever the psychology is and whatever I’m supposed to do myself, I’m actually trying to follow a historical line, because I knew that Rollo became a Count, and that was going to happen because I try to be as truthful as I can be.

Ragnar is comprehensively defeated by Rollo and his comprehensive defeat changes everything. It changes the nature of Ragnar’s life, what he chooses to do afterwards, and it has this wonderfully unexpected texture, that Rollo is victorious. Someone told me, “whatever I thought about Rollo, I didn’t expect him to be triumphant, but when this happened, I kind of liked it. I could respect it, because I expected to be sympathetic to Ragnar and yet when Rollo is victorious I kind of liked that.” And I understand that; I feel that myself. I feel good for Rollo — he deserves it.

How much time has passed between Ragnar’s disappearance after the defeat in Paris and the moment he shows up again in Kattegat to confront his sons?

We debated this a little bit, actually. We did one other jump forward in time in an earlier episode that worked very well and we didn’t want to stretch it too much. But nevertheless, it was very important to bring on Ragnar’s sons. So it’s something like six years. And Ragnar, after his defeat, he just disappears. They don’t know where he is and the sons are in a kind of vacuum because they don’t know he’s dead so no one can be king, so it creates an interesting dynamic. Everyone discussed this jump forward because it was dangerous and kind of problematic, but I wanted to do it very much. And I think that it works tremendously well when I watch it now. I’m enormously moved when Ragnar reappears in Kattegat and Kattegat has changed completely — it’s now a huge trading station and a different world than the world he left. I think it’s very moving.

What are the dynamics like between his sons? We see that they’re all very opinionated, especially Ivar.

I’ve invested a lot of time, hope and expectation in these sons. They didn’t have to carry the story forward themselves, because Lagertha (Katheryn Winnick) is still there, Floki (Gustaf Skarsgård) is still there and Bjorn is still there. So, we have a lot of standout characters who are still there. But nevertheless, it’s very important that the audience invest in these new characters. I think that straight off the bat, they’re going to be intrigued by Ivar, but I also think that Ubbe is a very interesting potential character. He’s a very good actor. He’s an Australian actor like Travis and I think that Ubbe has inherited a lot of Ragnar’s attitudes and beliefs, and he’s going to keep those alive, whereas Ivar is the dark side of the Vikings in a way, but because you never know what he’s going to do, he’s very unpredictable and he’s very dangerous. And he’s always going to be watchful. I’m already deep into writing Season 5, so I could tell you some of the things that Ivar does that would make your hair stand on end, but he’s always going to be dangerous. He’s always going to be provocative. But the other sons are more complex because Ragnar’s legacy is complex itself. I mean, Ragnar didn’t want to be a ruler and he wanted to establish a farming community — he was a farmer. So some of his sons turned more towards that side of Ragnar and the curious side, the explorer. But Ivar has decided that he is the heir of Ragnar because Ragnar chose him when he went back to England.

It was Ragnar’s great and only fear that his sons would become more famous than he was. And I think that because Bjorn went into the Mediterranean, he’s famous around the Mediterranean. But the most famous Viking that I’ve come across is Ivar the Boneless. And so Ragnar’s fears became true that his sons did become more famous than he was. Because until we made him famous in the show, whoever knew about Ragnar Lothbrok?

Bjorn has certainly become his father’s son over the past couple of seasons, and after the time jump, we catch up with him when he’s preparing for that trip to the Mediterranean — what’s ahead for him?

He had the most difficult childhood, with two overachieving parents — that’s really difficult to live with. So he went into the world to prove himself and he proved himself, but he has this travel bug and I think that’s really basic to Viking culture. I don’t read about this too much, but I’m sure it’s true — there were many reasons why the Vikings set off from Scandinavia, but one of them was curiosity, I’m sure. They had these amazing boats and they just wanted to see what the world was like, and Bjorn has that big time. He really has that [more], I think, than Ragnar. I was writing about him today. He was in Sicily today and next week he’s going to be in Africa. He’s going to be in the Sahara Desert. So this guy just does amazing things and he’s a Viking from Scandinavia, for goodness’ sake. How did these guys do this? It’s awesome. So, he’s an awesome character and I’m so proud of how Alexander has portrayed him in real life. If you look at the show from the beginning, one of the things that you’ll notice is that Ragnar in the first season looks like a young guy and by Season 4, he doesn’t look like a young guy anymore. But Alexander, he was a puppy. When he first came on set I had to stop him smiling. I had to say, “You’re a Viking. Don’t smile all the time.” And now he’s really a serious person, a serious Viking and a serious explorer. It’s very exciting to take him to these new places and that’s what we’re gearing up to do now in Season 5.

We didn’t see Lagertha following the time jump, so what can we expect from her in the back half of Season 4?

I wish I could tell you. [Laughs.] Lagertha is so important to the show; Lagertha is in some ways now the soul of the show. She does something so extraordinary in terms of reclaiming what she thinks is her own. And it’s a huge move that she makes and it will determine her life and a lot of other people’s lives. But she makes a huge decision to take back her own life and she really imposes herself on the landscape of the show.

Did you structure Season 4 in terms of two separate story arcs, given the fact that History doubled this season’s episode order, or do the two halves have a cohesive throughline?

Yeah, it didn’t faze me when they suddenly ordered more episodes. I wanted to do more episodes. I’ve always had a long-term view about it. I know in my mind where I want it to end. I’ve just kind of crossed my fingers and hoped that we can push it forward. Of course, you’re dealing with a commercial entity. This is a network show. You have lots of cliffhangers here to accommodate the format, but I’ve always had a long-term plan, and I thought it was really clever when I discovered a lead character who had lots of sons, so I can take this story forward. [Season 4] is all of a piece. The challenge for me is always to make it engaging enough, human enough and dramatic enough, I guess, for people to keep watching.

We don’t know what Ragnar has been doing during those missing six years — what can you preview about how time has affected him and what we can look forward to in the back half of the season?

I’m not going to give anything away, but I would say that the storylines of Ragnar and King Ecbert (Linus Roache) coincide, finally. So two of the greatest characters in the show come together and in a most extraordinary way. This is the best thing I’ve ever been involved with. There are a couple of episodes in Season 4 that are the best things I’ve ever written and affected everybody on the show, and I can’t wait for people to come to these episodes, but they’re still unexpected. You can’t second-guess what’s going to happen, but it’s just so emotional and as I say, I’m prouder of where we’re going with these episodes than anything that I’ve ever written. I want people to be there, because Season 4 will be startling and extraordinary.

What did you think of the “Vikings” midseason finale? Weigh in below.