Evil Twin by Kati Wilde

Bane should have been king… But he was born four minutes too late. Though it was Bane who’d led armies to victory against the scourge of the undying, now he must watch as his undeserving twin claims yet another throne through marriage to a princess of a neighboring kingdom. A kingdom that Bane had saved.
That throne should be his. So he’ll take it.
All Bane must do is deceive his twin’s innocent bride. He’ll trick her into his bed, and once he’s planted his seed, the bride—and her kingdom—will be his. With such a prize in hand, he won’t care if she ever forgives him for his deception. It hardly matters if she does, because his evil plan doesn’t include falling in love.
But his bride has a few plans of her own…