Sea Dragon Heir

In a world beyond time, the Palindrake family rules the rocky kingdom of Caradore, their right ordained by their allegiance to the power of the sea. But war came to them, and defeat at the hands of the king of Fire. For generations the Palindrake Lords served the god of Fire.

But now, five lifetimes later, the Palindrake heir, Vlraven V, has a twin sister, a woman who embodies their inheritance of power in a way that no wife ever could. The tidal power in their blood draws them to each other, into a forbidden passion that cold sweep away the bonds of fire placed upon the oceanic magic of the sea, and free Caradore from its long imprisonment.

Synopsis from Open Library.