Who was Shwetaketu's biological father?

Question

One of the most famous parts of the Chandogya Upanishad is the dialogue of the sage Uddalaka Aruni with his son Shwetaketu. (It's known as the Sad Vidya, and it's one of the 32 Brahma Vidyas.) It is during this dialogue that the famous Mahavakya "Tat Tvam Asi" or "Thou art That", which plays an important role in Advaita, is mentioned. (See my question here for how other schools interpret the Mahavakyas.). But I'm interested in Shwetaketu himself.

Shwetaketu is known for many things. He was the one who abolished polyandry, the practice of a wife having multiple husbands, as described in the Adi Parva of the Mahabharata. (A husband having multiple wives, on the other hand, is a well-established practice.) And he was the uncle of Ashtavakra, the purported author of the Ashtavakra Gita. And he is said to have written a text which formed the basis of a certain work of Vatsayana. But my question is about Shwetaketu's parentage.

This chapter of the Shanti Parva of the Mahabharata describes how certain acts, which are usually grave sins, are allowed in certain circumstances. In particular it says this:

Connection with the preceptor's wife at the preceptor's command does not stain the pupil. The sage Uddalaka caused his son Swetaketu to be begotten by a disciple.

My question is, who is Shwetaketu's biological father? This is a case of Niyoga, which is the practice I discuss here where a woman has a man other than her husband father a child with her, either because her husband is unable to father children or because he's dead.

So who was the disciple that Uddalaka Aruni chose to bear a child on his behalf? Is this story of Shwetaketu being born through Niyoga described in more detail in any other scriptures?

Also, on a side note if Shwetaketu was born through because Uddalaka Aruni was unable to have children, was his daughter Sujata, mother of Ashtavakra, also born through Niyoga?