Fire King by Milly Taiden

Running is Chelsea Golby’s escape. Literally. She runs to get away from the pain of being rejected after asking the love of her life to marry her. Instead of wallowing in self-pity, or a pint of Ben and Jerry’s, she heads to the Crystal Kingdom to hang out with her sister Avery, the new Elf Queen. With Avery busy being queen, she decides to go on a run to see the magical lands. Maybe what her grandmom said was true and Chelsea has magic in her blood too.
Zaos Firefoot,the right hand man to King Gorwin, knows his people are fading out. It’s too bad he can’t tell the dumb-ass leader exactly what he thinks about how he rules the kingdom. As much as he hates it, Zaos does what he’s told. Until the day he’s sent out to question and kill a light elf. When Zaos finds out that beautiful light elf is his mate, all bets are off with the killing thing. He’ll protect Chelsea with his last breath if necessary. Afterall, she’s his.
The surprises don’t stop at finding a mate. Someone forgot to tell Zaos he’s the son of a dragon and a Dark Elf who are mortal enemies. The drama explodes until the realm is at risk and everyone’s life is at stake. But Chelsea isn’t one to sit idle and watch. She’s about to learn that saving a world can get a girl killed. And it’ll destroy Zaos to know there’s nothing he can do to stop her.