Reine's counterpart

ROI

In French chess, this piece sits beside the queen and wears a crown.

"Reine" is the French word for "queen," so its natural counterpart would be the king. In French, "roi" means "king," making it the direct equivalent. The clue plays on the idea of opposites in royalty, assuming some basic French vocabulary knowledge. It’s a straightforward translation with no hidden wordplay.