Ancestry of Janduin
His ancestry is known from Rand's visions in the ter'angreal of Rhuidean.
Janduin was said to be the youngest clan chief in memory. A charismatic and gifted leader who was listened to and followed by not only his own people but others not of his clan. He ended the two hundred years long blood feud between the Taardad and Nakai clans and made alliance with them, as well as with the Reyn.
He wanted to end the blood feud between the Shaarad and Goshien, and might have had Laman not cut down the Tree. He led the Reyn, Nakai, Taardad, and Shaarad to the Westlands to seek Laman's bloodprice, which led to the Aiel War.
It is not known how and when he fell in love with Shaiel, Rand's biological mother, but Shaiel never married him, as she was told by Gitara Moroso's Foretelling to become a Maiden and had she married Janduin she would have had to leave the Maidens. She had become pregnant with Janduin's child in the beginning of the third year of the search for Laman. Maidens are forbidden by law to carry the spear while pregnant, but Janduin was deeply in love with her and unwilling to make her obey the law. In the Battle of the Shining Walls, she died giving birth to their son, Rand al'Thor and fulfilled the prophecy.
born of a maiden wedded to no man.
He will be of the ancient blood, and raised by the old blood."
— Karaethon Cycle
Janduin, believing both his lover and child were dead, could not forgive himself and forsaking his place as clan chief – something no one had ever done before – and journeyed into the Blight to slay shadowspawn. Those who returned said he encountered a man who looked like Shaiel, undoubtedly Luc Mantear, and refused to lift his spear when he was attacked.
Rand learns about his biological parents first from Amys, after he returns from Rhuidean. At that point in time he does not learn about the Andorran blood line, he only knows that he had a golden-haired not-Aiel mother and he had/has a half-brother. He is also unaware of the fact that they have already met in Caemlyn.