Before the Kurukshetra war Arjuna visited Alkapuri to seek divine weapons from Gods to prepare for the inevitable war. There he met Apsara Urvashi, who got infatuated with him and made advances towards him. Arjuna however, stopped her saying he considers Urvashi like his mother and cannot respond to her advances. Hearing this Urvashi got angry and cursed Arjuna to become a neuter and live among women as a dancer. 

When Arjuna told Indra about this curse, Indra convinced Urvashi to reduce the period of her curse to one year, so that it can help Arjuna to liveing in disguise during their one year of incognito period. 

Because of this curse Arjuna lived in Matsya kingdom as Brihannala during their one year of Agyatvas. 

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