[Denker]

Spoiler for Quote:

Originally Posted by Roberto1

I didn't even know he was a noble now, i never thought he would accept such thing XD

Sorry. I totally forgot about the spoiler tag. Long story short:

Spoiler for Rio:

Rio went to a party of nobles to get info. It was assaulted, and Rio participated in restraining them. It impressed everyone to the point of picking the interest of the King, the Second Prince, The Princess (among others)

Well, it seems that things like the letter and such are openly talked, and you yourself knew. Something that happened in Vol. 10. So I guess is not that bad to spoil important events like Rio being a noble.
That's pretty much how he revealed his identity as Haruto after all.