Rationalist, are you talkig about Veda Vyasa's Mahabharata? If so, Pandu was ruling on behalf of Dritarashtra. Both were sons of Veda Vyasa born to Amba and Ambika. The third brother (rather half-brother is Vidura - born to the maid of one of them).
The story in the form of narration by Vaisampayana at the funeral of Parikshit, the last Kind of Kuru Vamsa.
