The Saga of the See-ers. The Assassin's Apprentice. The Royal Assassin in 2 Books

Fitz is the illegitimate son of the hereditary prince. Raised by servants, he grew up in the dark corridors of the royal castle, knowing neither honor nor glory. His path awaited him as an assassin, faithfully and devotedly carrying out... the orders of his king, as well as the fate of a man capable of shifting the wheels of the world with his perhaps not very significant actions and setting into motion forces beyond the understanding of ordinary people... But that is why he is Fitz Chival See-er!
Fitz managed to accomplish a dangerous mission as the royal assassin, but it cost him too much. Miraculously surviving an assassination attempt, he vows not to return to royal service. But love and cruel circumstances draw him back to Buckeep, to the court of the aging and sick King Shrewd, into the sinister web of intrigues, into a war against the enemies of the Six Duchies that is flaring up with new strength.