He knew he was a prince from the beginning, he was the one who sent people to kill them.
He sent his people to kill them, but he wanted them ALL to die. Then he finds Kasan and his cover was as a slave to the royal family. And the Master treated him as such and beat the hell out of him and so forth. Then he starts to be nice, then it turns out there was survivor. I thought it was referring to Kasan (since we know he's a Prince) but I thought the Master didn't know. I thought the Master was still under the impression that Kasan was a slave. Instead he knew all along that Kasan was a Prince of the family he hated.
At least, that's what it looked like to me.
He knew it all along, that's why everybody says not to let Kasan know that the master was the one who killed his people and family. The master just have always wanted to humiliate Kasan as one of the same blood he hates. He thought Kasan was the only one who survived until things happened...
I re-read the story.
In chapter 1 we are told that Lord Igen requested at least 1 Azkun person be alive. We are told that Lord Igen had a feud with the Azkuns from 10 years back and that they were executed yesterday. There was 2 survivors but the woman resisted so they killed her. Kasan is referred to as the Azkun slave. And Azkun could refer to the family itself or the entire household (like I thought it did).
At the end of chapter 1 it has been 2 months since then. There is an assassin who is caught in chapter 2 who says that their young master lived. Igen asks if there was another survivor other than the slave that they took. Later on he refers to the other survivor as 'the seed of the Azkun family' as if he is only one of the family alive. Then his thoughts center on how he will use Kasan as bait.
So yeah, from re-reading it is clear that Kasan is the younger son of the family and Igen knows that. But it wasn't when I first read it because it always seemed to me, that Kasan was alive because he servant of the Azkun family. Because I thought they were referring to the household not the family. Even in chapter 3 the servant says that everybody in the Azkun family was killed, except the eldest son. Then Igen says now there is two people who have that dirty blood that have survived. Then Igen's thoughts say that Kasan is the younger brother.
Anyone else shocked that the Master KNEW he didn't have a slave but a Prince in his custody? How long has he known Kasan was a Prince? From the very beginning? Then what was he planning to do with Kasan if the First Prince didn't get away?