User blog comment:Sim0n2170/Attack on Titan Season 2 announced for SPRING 2017/@comment-5774380-20160703133127/@comment-5774380-20160703203401

@AhmedHadi1: That's what I meant with "four years after Season 2". S2 is airing in 2017, four years later is 2021. If the manga ends in 2018 (closer to 2019 actually), then a reasonable time for S3 release would be either late 2019 or early 2020 at most. If it gets delayed to 2021, that's not attributable to the manga, but solely due to Wit Studio wasting their time with their AoT clone (or another clone of another series) again.