A curse of queens / Amanda Bouchet.

Enhanced descriptions from Syndetics:

Discover an all-new adventure in USA Today Bestselling author Amanda Bouchet's thrilling, white-hot fantasy series featuring the king's younger sister and his best friend, the man she's loved in secret for years.

THE WAR OF GODS IS JUST BEGINNING

After centuries of conflict, the three kingdoms of Thalyria have finally been reunited. But now the queen has been cursed, the royal lineage has been broken, and no one knows who's behind the plot to threaten the once-fractured realm's fragile new peace.

Desperate to help, Jocasta--the king's younger sister and a gifted healer--hatches a daring plan to find Circe's Garden, a fabled island where she hopes to discover an antidote. But she can't do it alone. She needs the strong arm and unflinching bravery of the warrior she's loved since childhood--her brother's right-hand-man and captain of the guard, Flynn of Sinta.

Flynn has spent years fighting to deny the desperate longing burning between them, but he cannot allow Jocasta to face this danger alone. He swears he will be her shield, and together they will do the impossible. Yet with old feelings blazing bright and treachery brewing on Mount Olympus, one thing is clear: Thalyria and its new royals are still pawns in an epic game of power--one that might end in a War of Gods.

The Kingmaker Chronicles:

A Promise of Fire (Book 1)

Breath of Fire (Book 2)

Heart on Fire (Book 3)

A Curse of Queens (A Kingmaker Chronicles novel, Book 1)

Readers are raving about the Kingmaker Chronicles:

"Give this to your Game of Thrones fans."--Booklist STARRED Review

"Loved it!"--ELOISA JAMES, New York Times bestselling author

"Utterly breathtaking!"--DARYNDA JONES, New York Times bestselling author

"Masterful worldbuilding."--Kirkus STARRED Review

"Absolutely fabulous."--C.L. WILSON, New York Times bestselling author

"Easily my favorite book of 2016!"--Bookriot

"Delivers with both heat and heart--loved it!"--JEFFE KENNEDY, award-winning author