I found the name about the uncleXbrother pair...at least i think so :D It's called "Royal ...

Okay found something

Royal Fiance - Black Prince has already been released. This is actually the full name of the the manga you read. When you look up the manga's title in Japanese it will correct you. For some reason English sites cut off the second half of the name.

So, Royal Fiance - Black Prince is a manga, and you read it. Royal Fiance - White Prince is a light novel, and you haven't read it. Both have been released and finished 2 year ago. But the light novel was not translated yet >.<