Vikings: 8 Most Insane Fan Theories

This one sounds utterly bonkers, but there was a time when the concept of Rollo being Bjorn's father would sound equally crazy, so perhaps it isn't too unreasonable. There is some decent evidence to back this theory up, and although the show never delved into it, it's possible that some factors could convince you a little.

Firstly, Ivar has black hair, which neither his mother nor father did. Additionally, the actor playing Ivar in childhood was a bright blonde, but this was retconned when Alex Høgh Andersen took over. Theorists believe this was a deliberate ploy to reveal his suspicious conception, as every other son resembles Ragnar and Aslaug in some way.

Furthermore, Rollo went out of his way to send troops to help Ivar in season five, but the show never revealed a connection between them. Why would he help Ivar out when it put Bjorn at such risk? Possibly because he wanted to aid his real son.

Finally, Aslaug and Rollo did live together for some time after Kattegat was usurped and Ragnar was away in season three, right before Ivar was conceived, so it's not a huge leap of logic.

Of course, the show never addressed this, and although there is some compelling evidence, the theory doesn't seem too stable. But it's an intriguing thought that could have some major ramifications for every character in the show.