Complex sentence: The exact date of his birth is unknown as there are no records available, what is known of his origin is that he was born as the product of a relationship between an American soldier and a Cambodian refugee during the Vietnam War.
Split into simpler sentences: The exact date of his birth is unknown as there are no records available. What is known of his origin is that he was born as the product of a relationship between an American soldier and a Cambodian refugee during the Vietnam War.