Let me make this clear.
Sabo is a noble of the Kingdom of Goa. Not a World Noble.
His parents wants him to marry the Goa princess so their house can be set in stone as related to the royalty.
The only time the World Noble (Tenryuubito, Celestial Dragons) has been mentioned is the end of last chapter, and they have not played a role in this flashback yet.
That part is most likely yet to come, since all flashbacks must have a huge tragedy at its climax.