SOLVED. YA Fantasy book, read it about 2008 or 2009 at my highschool library, told from secondary character's pov, about a slave boy making his way through the ranks as he grows up. [s]

[Kaitie]

The narrator adores him because he is honorable and fair and smart.
He is killed by the princess's actual lover even though he was llanning on letting her marry her lover anyway but he never got a chance to make that known. I remember a specific part in the beginning of the book where the narrator, who is older than the main character, is teaching the main character to swim so he doesnt drown when their master throws him in the next morning.
After his death the narrator avenges him.

[SBC]

Is it The Wings of a Falcon? (aka The Tale of Oriel)

[Kaitie]

Oh my god.
This has been killing me for years.
YES, that is it!

[Kris]

Glad you found your book, Kaitie.

The Wings of a Falcon (book 3 of the Tales of the Kingdom series) by Cynthia Voigt - SBC's find.

[SBC]

I'm glad I could help! This book comes up quite a lot in this group. Lobstergirl noted in a thread in 2017 that it had been requested 7 times at that point, and I think I've seen it come up about 5 or 6 times since then. It's a memorable story (but hard to remember the author/title!)