Now that Attack on Titan finally ended, fans still wonder who was the father of Historia’s child. A lot has been said about how important Historia's child was and would be, but she barely showed up in Attack on Titan: The Final Season and The Final Chapters. Ironically, the same fate befell her mother. Because of Historia's absence and lack of resolution in the anime's final arc, many fans continue to wonder if Historia's child had any impact on the story, or if she even had a reason to exist.
Source：https://www.cbr.com/attack-on-titan-theory-historia-baby-eren-father/
