When did Duryodhana know that Karna is actually one of Pandava's brothers and a son of Kunti (Kuntiputra) and how did he react?
Duryodhan never knew that Karna was the son of Kunti, because Kunti revelaed this truth after finishing the war means Duryodhan was already dead when kunti revealed the truth to pandava.Source [https://www.youtube.com/watch?v=Ll2MVIZONgg]
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