That's not the real Doctor Sun, it's an impostor impersonating him
And yeah, it's AoAo. The difference between AoAo and his past self, Ao Yue (also known as Xuan Yue) is that Ao Yue/Xuan Yue was disowned and taken away when he was a baby, so he didn't know he was a prince and Ao Gu's biological younger brother. Ao Yue died and was revived as baby without memories, found by Ao Gu, renamed AoAo and taken back to the palace to be raised as a prince this time around.
In addition to the "different Ao Aos at different times" thing, Ao Ao is the second prince because he is the younger son of the dragon king. Ao Gu, the eldest, is the first (or crown) prince.
Ok that made is sm more clear tyty~
Ok so in chapter 64 Mr.Sun calls AoAo "Second prince";, is that AoAo the same AoAo from the school parts or is that AoAo a different reincarnation since Mr.Sun calls him "second prince". Or is is because Mr.Sun only knows him as that since Ryan is also there?? IM SO CONFUSED HUHU TT