While walking on the banks of the river Shantanu saw a beautiful maiden, Ganga, charmed by her beauty he proposed Ganga for marriage. Ganga accepted his proposal upon one condition- That he must never question her about any of her actions. As he was in love, he thought it would be a small request after all and agreed immediately.
They lived a happy Married life, and soon Ganga was pregnant but as soon as the child was born, she drowned the new born baby in the river Ganga. And the same happened with the next 6 children too. When she was about to drown the 8th child, Shantanu stopped her and questioned her thus breaking his promise.
Ganga then explained him how the 8 vasus were cursed by Sage Vashishta and had requested her to immerse them in Ganga to free them from the curse. The 8th child born was Prabhasa, and he was cursed to live long as he stole Nandini, but the Sage had also given him a boon that, he would be known as one of the important persons in the holy scriptures. Saying this Ganga, took Devavrata, the 8th son, and said, she would return him to the king after training him for the King’s status and left.