Spoilerrr
Griz did know from the start that he was the Chuni kid. MC was killed by the other knight in Griz's order, the one that saved MC in the alleyway, it was an order from his family iirc. Griz does regret their last encounter and goes searching for MC for the next few years, there was a war in which he participated in because the other country claimed to have the special child and he thought that it was MC, only to be disappointed.
No, he doesn't. He thinks MC ran away bc there was no body left when MC was killed, and the killer didn't make it a point to be like "I killed MC!" I'm not rooting for Griz either cuz he liked MC since the beginning, as the chuni kid but MC was like 12-14 and he was an adult already like 20ish. The authors made it a time skip so they're similar in age.

Can a kind soul plz spoil me on whether griz knew from the start he’s the chuni kid and who killed him in his first times there? Plus if there’s some regret arc or smthg (I was reading waiting for the regret but it’s all fluffy )