Heart of Thorns by Leigh Kelsey

The cruel fae queen won’t stop until Maia is captured … or dead.

Maia always knew Ismene was wicked, but her aunt is even more monstrous than she feared. Responsible for countless deaths, Ismene will stop at nothing to protect her reign. And Maia just made herself the queen’s most wanted foe.
To stay free, Maia will have to disappear. She’s taken refuge with Azrail—the Sapphire Knight—and in his home, she discovers a rare, unexpected joy: Jaromir, the sweet jaguar shifter who’s her fated mate. But being Jaro’s mate won’t save her if Azrail discovers the truth: she’s not just a librarian, she’s the princess of the Vassal Empire.
His sworn enemy.
As evil spreads across the City of Skies like a shadow, friends will become enemies and enemies will become friends – and ancient magic will be reborn.