secret story; untold episode
Refers to a story or episode that is not widely known, often with historical or personal significance. Common in titles like 歴史の秘話 or 皇室の秘話.
I heard the untold story behind the founding of this company.
This book is a collection of secret stories from the Warring States period.
He told a secret story that he had only shared with his family.
He revealed the untold story behind the making of the film.
The long-hidden secret story finally came to light.
逸話 is an anecdote or interesting episode about someone, not necessarily secret, whereas 秘話 emphasizes that the story has been hidden from the public.
裏話 is a casual 'behind-the-scenes' story shared informally, while 秘話 carries a stronger sense of a formerly concealed, often significant, story.
untold story behind the creation; secret origin story
Compound of 秘 (secret) and 話 (story, talk). The reading ひわ is the standard on'yomi combination.