Crown Prince
noun
The emperor's fat child is the crown prince, not because he's fat, but because he's the emperor's child.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
皇太子殿下に「うまくいくといいですね」と言った。
I told the crown prince that I hope things work out for him.