Harry Potter and the Prisoner of Azkaban
"Dumbledore told them that their best chance was the Fidelius Charm."
"An immensely complex spell," he said squeakily, "involving the magical concealment of a secret inside a single, living soul. The information is hidden inside the chosen person, or Secret-Keeper, and is henceforth impossible to find – unless, of course, the Secret-Keeper chooses to divulge it." (10.3.147-149)
Why had nobody ever told him? Dumbledore, Hagrid, Mr. Weasley, Cornelius Fudge [...] why hadn't anyone ever mentioned the fact that Harry's parents died because their best friend had betrayed them? (11.1.2)
Snape's sallow skin had gone the color of sour milk.
"And did the headmaster tell you the circumstances in which your father saved my life?" he whispered. "Or did he consider the details too unpleasant for precious Potter's delicate ears?" (14.3.78-79)