User blog comment:Skeith9/Heroic Spirits Speculation/@comment-25119196-20140629111230/@comment-24762556-20140630070030

Odd, at least from the version that I've know, Arjuna and Karna both knew they are brothers quite a while before their final duel, or at least Karna definitely knew that Kunti is his mom way long before his final duel with Arjuna. It was supposed to be one of Karna's main personal conflict that he has to fight on Duryodhana's side even after learning that the Pandavas are his brothers, including Arjuna who had already been his archrival for quite a time at that point and both had already sworn to kill each other. When Hindu heroes swore something, they never take their words back even after learning that the opposite side is a family member, at that was supposed to be the premise of their final battle and the core purpose for Karna as a tragic character.