Krishna takes leave of Kunti, the elders and kauravas. Then invites Karna to join him on the chariot. Once they are out of the city Krishna addresses Karna with a purpose, 'Karna! You have served Brhamins who are authorities in Vedas and have learnt from them the complexities of our dharma shastra. You know that a सहोढ, a youth born to an unwed mother, becomes the son of the man she marries later. You, born to a very young mother, are Pandu's son as per this dharma. You are the eldest! Hence the kingdom should go to you. Both pandavas through your father and vrishnis through your mother are your family. So come with me! Pandavas will respect you as their elder brother. Draupadi and Subhadra's children and kings aligned to pandavas will pay homage to you. In time Draupadi will think of you as her sixth husband. I will install you as the king and Yudhisthira as the yuvaraja. Pandavas, Panchalas and Vrishnis will all be your subjects. Like the moon among the stars rule the kingdom. This will please your mother and your well wishers!'
This is an emotionally charged moment for Karna. In Kamala's version he even faints when learns from Krishna that Surya is his father. But he is not tempted by Krishna's offer. He still wants to be true to his friendship with Duryodhana and is happy to be the son of the woman who took care of an abondoned child with so much love!
Vachana Bharata is a bit different:
Karna knew all this, as Surya appeared a day before, told him who he was and had warned him to be careful as Indra might come and ask for his Kavacha and Kundala so that Arjuna could be saved.
Karna replies, 'Yes, I know about my birth. But Kunti abondoned me in a manner that could have been perilous. Athiratha, a suta, found me and picked me up with love and took me home. The moment Radha saw me she was filled with tenderness and as she held me in her arms, she began to produce milk! Should I not take care of her as a son and be there for her last rites when the time comes? Athiratha loves me as his own son and this love is reciprocated by me and I consider him to be my father. Because of this love, he has performed all the rituals as per the shastras and has given me the name of Vasushena. He got me married at the right time, and I have children and grandchildren and I am fond of them! I have developed good relationships with the sutas.'
'Even if I am given untold wealth or offered the whole earth, I cannot tell a lie. I have been very happy as a king the last thirteen years in the kingdom provided by Duryodhana. It is because of his trust in me, Duryodhana has decided to wage a war. I have to face Arjuna in a combat, if not we both will get a bad name! I know that it is in my interest and I assume that pandavas will listen to you. The moment Yudhisthira learns that I am Kunti's son, he will not accept the kingdom. If it is given to me, I will give it back to Duryodhana! So, let the Virtuous Yudhisthira rule the kingdom. I am sure there will be a great war, which will end only when Bheema kills Duryodhana. The kaurava women will shed tears at the final parting of their men! '
'Conduct the war as you wish. But let the elderly khsatriyas be saved and the large clan of khsatriyas fight and attain heaven in this war. Bring me and Arjuna face to face. Let this conversation be a secret'
Krishna smiles at Karna, "So you have no desire to be a king and rule the kingdom I was planning to get you! Let it be! There is no doubt that pandavas will be victorius. You will soon face Arjuna in a war. When you return, you can suggest to Bheeshma and Drona that 'The season is right. The weather is mild. The trees are full of fruits. The earth is dry, there is enough water and insects are not too many. Seven days from today is the new moon and we can begin the war on that day'. The kings who are under Duryodhana will all die in the war and attain सद्गति the happy state.
Karna says that he is aware of this as he has seen many ill-omens and bad dreams already. 'I do not know if we will ever meet after this destructive war!'. Karna then embraces Krishna and gets off from his chariot and climbs on his own and retuns with a heavy heart. Krishna and Satyaki also leave and urge their charioteers to make haste!