Dark Angel by Felicity Heaton

Centuries in Hell have taken their toll on Apollyon. Tired of guarding the Devil, he longs to break free of the dark realm. The trouble is, he can’t leave without permission. When he feels someone calling him, he seizes his chance for freedom, but what awaits him in the mortal realm is the last thing he expects—the beautiful woman he has watched over from Hell, a witch who casts a spell on him and awakens the darkest desires of his heart.
Serenity is shocked when a wickedly sensual black-winged angel shows up in her city of Paris claiming that she summoned him when she was only casting a simple vengeance spell. He’s no other than the angel of death! A very gorgeous, alluring angel of death who makes her feel she’s in danger of getting her heart broken all over again.
When the lethally handsome warrior offers to obey her and give her revenge, Serenity can’t resist the temptation, but can she resist the forbidden hungers the dark angel stirs in her?

Note: This is a revised, extremely extended and re-released version of Her Dark Angel after a rights reversion.