Identify fantasy story with magical boy, girl who marries a prince who is assassinated

Question

I'm trying to identify a book, or possibly series, which I read when I was in secondary school, in the early 2000s. I got it out of my school library - it was recommended to me by the librarian - which I remember being surprised by due to the content. The nature of the parts that I remember well will give you an indication of the preoccupations of my teenage mind at the time...

I recall:

• A protagonist who is a young common boy who has inherited magical ability?
• A traditional evil scheming bastard of a royal adviser, who I shall call Vizier. Possibly also a wizard
• A King and Queen with a legitimate heir, Okay Prince
• Vizier takes advantage of an opportunity when the King is away to drug and rape the Queen, with the goal of fathering a child to be a prince to fulfill his plans, which succeeds (creating Bad Prince). During the act he is pleasantly surprised to discover he's sufficiently aroused by the situation to do the deed without a bunch of faffing about (he's really weird)
• Pretty sure Vizier also kills the King somehow, after making sure it is plausible that the King could have fathered Bad Prince.
• Another protagonist who is an innocent girl who marries Okay Prince, but he is assassinated (I want to say poisoned) in their chambers on their wedding night. It is an important plot point that, unbeknownst to anyone else, their marriage WAS consummated, because they were so eager they had sex on the stairs on the way up, and I think she becomes pregnant too. She flees the situation afterwards and goes into hiding?
• Bad Prince is really not well adjusted; has an obsession with purity and a tendency to homicidal rage
• Bad Prince is married to another girl who turns out to not be an innocent virgin at all, so he flies into a rage and beats her to death (specifically, she waits for him in bed lying spreadeagled with makeup applied in unusual places, thinking that her previous lover would've loved it; Bad Prince thinks she looks like a whore)
• At some point there are two guards/stablemen having a conversation about the effects of alcohol on sexual ability, with one of them insisting that there's a special stage of advanced drunkenness that can be reached by drinking enough which sees you go through impotency and come out the other side as a "raging stallion"

I have no idea if these works were actually any good, as my ability to distinguish decent from dross at that age was surely lacking, but for some reason the story popped back into my mind recently. I don't remember a conclusion, so I suspect it may have been a series of books I did not finish reading rather than one self-contained novel.

Answer 1

The Baker's Boy by J. V. Jones, the first novel in The Book of Words trilogy.

From the synopsis in the above link:

The tale begins with a glimpse of a truly despicable villain at work. Baralis, as you will come to know him, is a man who will do anything to succeed. A master of potions and poisons, he drugs the queen's wine and rapes her in the dark of night. A child is born from the terrible ill-fated union: a monster, obsessed, close to madness, destined to rule over half a continent.

It has been a long time since I read it, but the timing is right (first published 1997) and I believe it hits most or all of your other bullet points as well.