untold story behind the creation; secret origin story
Refers to the hidden or little-known background of how something came to be, often used for products, works of art, or events. Carries a slightly dramatic or promotional tone.
Hearing the untold story behind this movie made me like it even more.
The secret origin story of the new product was revealed on the official website.
秘話 is a general term for a secret or little-known story, while 誕生秘話 specifically refers to the story behind the birth or creation of something.
裏話 is a behind-the-scenes story, often with a gossipy or insider tone, whereas 誕生秘話 focuses on the origin and creation process.
Compound of 誕生 (birth, creation) and 秘話 (secret story). The exact origin of the compound is uncertain, but it likely emerged in modern Japanese media to describe the hidden background of notable creations.