Cuòguò nà ge jīhuì chéng le tā xīnzhōng de hènshì.
Missing that opportunity became a deep regret in his heart.
Tips
register
Literary/written register. 恨 here means “regret; lasting grief,” not just “to hate” — closer to the older sense of 遗憾 (yíhàn). Common in classical novels and biographical writing; rarely used in casual speech.
