ya sci fi about three teens from different planets taken by a planetary overlord /s

[Donna]

I remember this book had a dark cover with stairs, and the only parts I can remember clearly is that outside the overlords home(castle?) was a nova. Its from the p.o.v. of the boy, one girl come from peace no kill planet and other was a princess of a tribe. this book was written before 2000.

[Sue]

This reminds me of 'Ben-Harrans Castle' by Louise Lawrence.
"Two teenagers are taken from different worlds to Ben Harren's Castle, which travels within the boundaries of Ben-Harren's galactic territory. Kysha is from a perfect world, Erinos, while Christopher is from a planet struggling with free will. The teenagers' task is to judge their hosts."

[bookel]

Ben Harran's castle (USA title: Keeper of the universe) by Louise Lawrence.

[Donna]

that's it!!! thank you I've been on and off looking for it for years.

[Ann aka Iftcan]

Congrats on the super fast find Donna. I've shelved the book and moved this down to Solved for you.