When does Allen Walker from d gray man finds that he is Noah?

Allen Walker discovers he is part of the Noah family during the events of the "D.Gray-man" manga, particularly in the later arcs. This revelation occurs when he confronts the truth about his own identity and the connection to the Millennium Earl and the Noah. The realization is tied to his struggles with his own abilities and the legacy of his past, ultimately leading to significant character development and conflict within the story.