Looking for a book where the main character is of another world, becomes a female and mute at the end

[Lexiegray]

I read this as a teen in the early 2000s... I think it's fantasy. I think there might be spells or something along the lines of spells involved. I want to say they might be aliens? Or there are humans but there are also a different species that live with them. What I do remember is that somewhere near the end, the main character is being held prisoner and the bad guy (or girl) tries to get him to reveal something by lowering a crystal down his throat. Main character knows that if he screams or yells, his voice will make the crystal break (or similar) and hurt him or kill him. Somehow at the end the main male character becomes a female and can't talk anymore, so no one knows who he used to be. I also think I remember he used to be some sort of prince or high ranking young adult... so when he is turned into a female, he also becomes like a handmaiden or something of the sort. I know it's a long shot. Thanks for any help!

 

[Danny McG]

Whaaaat?
Female and mute.
That is some way-out fantasy

 

[Vince W]

Whaaaat?
Female and mute.
That is some way-out fantasy

You may need some witness protection after that one.

 

[tachyon]

Found this: "I seem to remember that the main character may have undergone a magical sex change at some point."
Sci-fi series where humans are reduced to a mathematical pattern and sent to another planet