שמואל ב, פרק י״ג, פסוק ג׳

Amnon's inner circle included a figure who held a decisive influence over his choices. This man, Jonadab, was a close and devoted friend [מצודת ציון]. The bond was also rooted in family, as Jonadab was Amnon's cousin—the son of Shimeah, one of David's older brothers—and was likely the older of the two [ביאור שטיינזלץ].

Jonadab is characterized as a deeply wise man, a description that presents a challenge. Typically, when someone is simply called wise, it implies they use their intellect for good [מלבי״ם]. In this case, however, the commentators agree that Jonadab channeled his intelligence toward negative ends. He possessed a dark wisdom, using his sharp mind for wickedness and evil [רש״י, מצודת דוד]. His intelligence was highly practical and cunning; he was a shrewd thinker who knew exactly how to craft schemes and offer effective, yet completely immoral, advice [רלב״ג, ביאור שטיינזלץ].

This cunning influence played a crucial role in Amnon's downfall. Jonadab managed to persuade his cousin to commit an act that Amnon had initially found too difficult to carry out. The moment Jonadab offered his sophisticated plan, it stripped away Amnon's moral inhibitions, making him feel justified in fulfilling his dark desires [רלב״ג].