Board Thread:Manga/@comment-27125793-20190202152111/@comment-27125793-20190203155433

To be fair, it would be predictable only for us here who regularly use the forum to chat, since we share our theories with one another. For most regular readers, it would be a big twist.

This is the most likely scenario in my mind:

Eren, due to their friendship and a sense of obligation, warns Historia of the military's plan to have her eat Zeke the moment he lands on Paradis (him having been informed by Yelena, probably). She is either slightly horrified or mixed on the issue, and then Eren tells her of his plan to force the Survey Corps to attack Marley not just to save Paradis, but her and her children. Reluctantly, he convinces her to become pregnant to avoid her becoming the Beast Titan prematurely. She is unsure, not fully willing to trust Zeke and Yelena nor liking him going rogue and putting himself in danger. They discuss it (read: argue), and she eventually realizes that trying to stop him is not only pointless but detrimental to Paradis survival, in the sense that it would affect his standing and relationship with the military and the populace at a stage where it was too dangerous to do so. One enemy, who significantly outnumbered them, is a big enough problem as is. In either a last bid to convince him otherwise or a desire to have a child with someone close to her (or both), she says that she would keep his plans a secret if he agrees to be the father of her child. Flabbergasted and protesting Eren, stubborn Historia, more arguing, and he eventually caves. When he learns of her pregnancy, he becomes even more motivated to see his plan through, becoming stalwart enough to even kill innocent civilians.

There. Those are my thoughts. I think it would be quite clever if it were true.