Demonbreed by Lizzy Bequin

Men want her body.
He wants her soul.
Jenevieve is the heir to a dying kingdom. When she finds herself besieged by a barbarian army who intend to plunder her lands and her body, there seems to be no chance of escape.
Until she discovers a dark secret from the past:
A demon imprisoned by her father.
Cabael is a horned beast born in the infernal plane, a realm where pleasure walks hand in hand with pain. Even in chains, his muscled body exudes of an aura of dominance that threatens to bring the young queen to her knees.
He agrees to help Jenevieve with her problems, but as she quickly discovers, a demon’s aid comes at a price. And as she enters into a dangerous exchange of carnal favors with the monster, one thing becomes abundantly clear:
Cabael will not be satisfied until Jenevieve is carrying his unholy spawn inside her womb.