そして、同じくアニメージュ7月号で「ダイヤモンドは砕けない」は3クール全39話であることが明らかに…!一気に最後まで駆け抜けますよ! #jojo_anime すーじー
— TVアニメ『ジョジョの奇妙な冒険』公式 (@anime_jojo) June 10, 2016
What makes this news interesting is the fact that Diamond Is Unbreakable manga 18 volumes long, the 2nd longest in the series. Compare this to the Stardust Crusaders manga, the series was collected in a total of 16 volumes, and was adapted into 48-episode series.
[Source: Anime News Network]