Hajime Isayamaofficial creator of the manga, recently revealed that A prequel to “Shingeki no Kyojin (Attack on Titan)” was canceled for fear of ruining the series’ continuity.

Via Twitter, Isayama stated in the franchise's new art book that he originally intended to write a prequel, adding that “would take place 100 years before the main story». And he continued: “However, when depicting such a story, if there is a single discrepancy with the main story, it will no longer fit well. It would take a lot of determination to draw it, so I didn't make any progress in writing it.».

Isayama adds: «The events of the Angoulême International Comics Festival made me realize that the priority of this one-shot is to make fans happy. So instead of the original idea, I decided to make a one-shot that revealed something I had said I would draw before but hadn't drawn yet: 'Why is Levi holding a teacup in such a weird way?» The hypothetical prequel would join the other prequel novel “Shingeki no Kyojin: Before the Fall”, written by Ryo Suzukaze with art by Satoshi Shiki.

Instead of Isayama's planned prequel, fans were given volume 35 of "Shingeki no Kyojin," first announced last year and focusing on Levi. Meanwhile, the larger “FLY” art book included numerous illustrations and commentary from Isayama. Meanwhile, franchise creator Hajime Isayama remains active, overseeing a new story alongside Eren’s voice actor Yuki Kaji in the “Soyogi Fractal” manga series.

Source: Eren Cabin on Twitter