Nos had a few things going for him off the bat as far as securing the succession was concerned. Unlike a number of his siblings, he was actually in a proper position of power as the Kingdom's Steward. A vital pillar of the throne in that his job was to make sure that the King (or Queen) could ensure the loyalty of the other pillars by being able to buy it. 

And so he enjoyed a rather pleasant conversation with those appointed by his majesty to the highest positions of law enforcement in the land. They were natural allies after all; Without those that enforced the kings laws, the population would try to avoid paying their taxes and without the tax collector collecting that wealth and ensuring it reached those enforcers they would be forced to farm or tend to the land in order to provide for themselves and their families. Problems with one of them caused problems for the other and as such it was always a good idea to keep an eye out for the others well being. 

Of course, it by itself wouldn't be enough to just have their father declare them the heir. Tradition couldn't exactly be debunked so easily after all... but Nos knew that his father wasn't foolish enough to risk the future of the kingdom to mere chance. He got to select the challenges after all...

Through that did rise the question of where his Majesty currently was.