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In Star Plus Mahabharata (e.g., S11 E7), it is shown again and again that Karna believed that it was adharma to not appoint Duryodhana as King/Yuvaraja (crown prince) of Hastinapura.
Did Karna really believe so according to the original Mahabharata text? If yes, what reasons did he offer?
Note: This is not a duplicate of Why was Yudishthir considered to be the next King after Dhritrashtra and not Duryodhana? which is a general question about Duryodhana and his rights whereas this is more about what Karna believed and why.