After Moses died, he was succeeded by יְהוֹשֻׁעַ בִּן נוּן (Joshua, son of none). If Joshua had no parents, where did he come from?
Everyone who was at the revelation at Sinai and was considered a convert, and a convert is considered a tinok shenolad, without relatives (see the discussion abou ger who can marry his sister who is a giyoress). After Sinai Hashem explicitly set up the family and tribal relationships with "return to your tents".
Yehoshua was thus able to get back his connection to the tribe of Ephraim, but he lived in the "tent of Moshe". He was not yet married and he no longer lived with his parents. Thus he had no "father".
Another explanation is Yehoshua Bin No-one.
Since he was training to become the leader he could not fall into the same "bin" as the rest of Bnai Yisrael. He had to remain objective.
Another possibility is Yehoshua Bin Noon
Just as Moshe Rabbeinu took care of Bnei Yisrael from early morning, Yehoshua could only handle matters for himself at midday. This may have been because Moshe Rabbeinu was getting ready for Mincha and it was too late for Shacharis. Thus, Yehoshua had a break at that time.
This is caused by a misunderstanding of the word נוּן.
It actually means "fish" in Arabic and ancient Aramaic. https://en.wikipedia.org/wiki/Nun_%28letter%29#Origins
So, his real name is actually Joshua Fishson.