noun
sequel; later development; follow-up story
Refers to an account of what happened after a previously told story or event; often used for epilogues, afterwords, or updates.
小説の後日談が雑誌に掲載された。
A sequel to the novel was published in the magazine.
事件の後日談を聞かせてください。
Please tell me what happened after the incident.
その後 is a general adverbial phrase meaning 'after that', whereas 後日談 is a noun referring to a narrative about later events.
Compound of 後日 (later date) and 談 (story, talk).