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Uttara Kumar the son of King Virata was cowardly and had no qualities a prince should have had. When all the Matsya army set off to wage war against the Kauravas who were waiting at their gates, Brihannala offered to ride Uttar's chariot for him, while the later battled. Upon seeing the huge Kaurava army, Uttar, being timid natured, panicked and asked Brihannala to ride the chariot back to Matsya.
When Arjuna as Brihannala reminded him of his duties as a Kshatriya, Uttara begged that he'd take all the dishonour and misfortune on his head. When Brihannala tried to persuade him, Uttar ran away with the former behind him. Brihannala caught him back and told him that he was Arjuna and that he'd fight the Kaurava army. Meanwhile the agyatvaas ended and Arjun was transformed back to his original form. Picking up his Gandiva, with Uttar as his charioteer, he single handedly defeated the Kaurava clan.