When a fan took to Twitter to chastise John Green for using the word “retarded” in his novel Paper Towns, the wildly popular YA novelist offered a mea culpa.

Paper Towns tells the story of Quentin Jacobsen, whose neighbor Margo Roth Spiegelman goes missing after they share an adventurous all-nighter together. In the scene in question, a character says, “Sometimes he’s so retarded that he becomes kind of brilliant.”

The novel currently tops the New York Times Young Adult Best Sellers list, where it has spent 117 weeks. The film adaptation, starring Nat Wolff and Cara Delevingne, opens in theaters July 24.

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