SB 3.1.28

kaccid varūthādhipatir yadūnāṁ
 pradyumna āste sukham aṅga vīraḥ
yaṁ rukmiṇī bhagavato ’bhilebhe
 ārādhya viprān smaram ādi-sarge
Synonyms: 
kaccit — whether; varūtha — of the military; adhipatiḥ — commander in chief; yadūnām — of the Yadus; pradyumnaḥ — the son of Kṛṣṇa named Pradyumna; āste — is; sukham — happy; aṅga — O Uddhava; vīraḥ — the great warrior; yam — whom; rukmiṇī — the wife of Kṛṣṇa named Rukmiṇī; bhagavataḥ — from the Personality of Godhead; abhilebhe — got as a prize; ārādhya — pleasing; viprān — brāhmaṇas; smaram — Cupid (Kāmadeva); ādi-sarge — in his previous life.
Translation: 
O Uddhava, please tell me, How is Pradyumna, the commander in chief of the Yadus, who was Cupid in a former life? Rukmiṇī bore him as her son from Lord Kṛṣṇa, by the grace of brāhmaṇas whom she pleased.
Purport: 

According to Śrīla Jīva Gosvāmī, Smara (Cupid, or Kāmadeva) is one of the eternal associates of Lord Kṛṣṇa. Jīva Gosvāmī has explained this very elaborately in his treatise Kṛṣṇa-sandarbha.