The Burning Sky by Sherry Thomas (The Elemental Trilogy #1)

It all began with a ruined elixir and a bolt of lightning.

Iolanthe Seabourne is the greatest elemental mage of her generation—or so she's been told. The one prophesied for years to be the savior of The Realm. It is her duty and destiny to face and defeat the Bane, the most powerful tyrant and mage the world has ever known. This would be a suicide task for anyone, let alone a reluctant sixteen-year-old girl with no training.

Guided by his mother's visions and committed to avenging his family, Prince Titus has sworn to protect Iolanthe even as he prepares her for their battle with the Bane. But he makes the terrifying mistake of falling in love with the girl who should have been only a means to an end. Now, with the servants of the tyrant closing in, Titus must choose between his mission—and her life.

Genre: Fantasy