Is a convert's biological son obligated in "kibud av' (honoring his father)?

Question

This is the reverse of this question, in a sense.

Suppose that a Gentile intermarries and he has a son who is Jewish. Later, the Gentile converts. Is the biological son ever halachically obligated to honor his father?

There are, possibly, two factors:

1) There was no "halachically" valid marriage. So the "confusing mix", here, is that while the son was born to a Jewish mother making him Jewish, because this was an intermarrriage, there was no Jewish marriage and thus, perhaps the biological father is not halachically his father.

2) After conversion, the father becomes like a newborn and severs all previous family ties. Thus, his biological son is not halachically his son, anyway, now.

Answer 1

The Netziv (Rav Naftoli Tzvi Yehuda Berlin 19th century)in his Haskomo of Ahavas Chesed http://hebrewbooks.org/pdfpager.aspx?req=15141&st=&pgnum=7 (written by the Chafetz Chaim) speaks about the Mitzva of Kibbud Av Vaem as being 2 parts. The Logical obligation regarding Hakaras Hatov to the Parent for having brought the person into this world, and the "Chok" - Mitzva obligation that was specifically commanded to Jewish people in order to ideally fulfill in the Land of Israel. He says that of course even a gentile gets Schar for the logical Mitzva like Dama ben Nesina did. The Netziv concludes:

עכום הבא על בת ישראל והוליד בן ויש לו אם ולא אב מן התורה חייב בכבוד אב
A gentile who has a son from a Jewish woman, that son is still obligated Mideoraisa to honour his father whether he converts to Judaism or not.