In due course Devyani gave birth to two sons, Yadu and Turvasu. Sharmishtha gave birth to three sons, Druhya, Anu and Puru. Devyani did not know that Sharmishtha was married. Several times she asked Sharmishtha to reveal the name of her husband but received only evasive replies. She then called Druhya, Anu and Puru and was shocked to learn that they were Yayati's sons.
Devyani went crying to her father. True to his threat Shukracharya cursed Yayati that old age will set on him, though he was in the prime of his youth. Yayati was aghast and repentant. He said, "I am your daughter's husband. Do not impose such a harsh punishment on me. I am young and will not be able to live the rest of my life with this beautiful woman without enjoying sexual pleasures." Shukracharya replied, "I cannot take back my curse, but I can modify it. If any of your sons are willing to exchange their youth for your old age, it can be done."
Yayati went to each of his sons in turn. Yadu, Turvasu, Druhya and Anu rejected the proposal with contempt. The youngest son, Puru, however said it was his duty to fulfill his father's desires and ensure his father's comforts o he agreed to take Yayati's old age. For a thousand years Yayati lived a pleasurable life with his wives and after his passions were fully sated he returned Puru's youth to him. Some texts say that he had a rollicking affair with the celestial maiden Vishwachi as well.
In return for Puru's sacrifice he crowned Puru as the next king of the lunar dynasty and declared that his lineage would continue through Puru. It was in this dynasty that the warring cousins, the Kauravas and the Pandavas were born. Yadu started his own dynasty. Krishna, the eighth incarnation of Vishnu, who was the advisor to the Pandavas, was a descendent of Yadu.
The epic Mahabharata adds that after crowning Puru, Yayati lived the life of an ascetic and went to heaven after his death. In heaven he began to boast that he was the greatest. This irritated Indra, who sent him back to earth. On the way some wise men stopped him and while he was hanging midway, they learnt from him all the knowledge that he had acquired. He then spent some more time on earth, overcame his arrogance and went back to heaven - this time forever.