inside story; behind-the-scenes account
Refers to the real, often hidden or untold story behind an event, situation, or person. Commonly used in journalism, entertainment, and casual conversation.
その事件の裏話を聞いて驚いた。
I was surprised to hear the inside story of that incident.
彼は有名俳優の裏話をたくさん知っている。
He knows a lot of behind-the-scenes stories about famous actors.