Into the Ashes by Sophia Nye

A charming rogue falls for an off-limits ice princess.
Rescuing a captive princess is an average day for Diarmid O’Conor, a warrior of the Fianna so notorious for his charms that his fellow Fianna wager he can’t go a fortnight without a woman in his bed. Admittedly, winning the wager would have proven challenging under normal circumstances. But when Diarmid clashes with the rescued princess, he finds himself pining for the only woman he’s ever met who doesn’t return his affections.

Cara O’Donnell, Princess of Thurles, just wants to help her family keep their land by marrying the man to whom she’s betrothed. When the irritating Diarmid and his band of warriors deliver her to the man’s keep, however, he insults her by refusing the betrothal.
With the success of their mission at stake, Diarmid convinces Cara to let him help her win over her would-be betrothed by teaching her some of his charms. They fully expect the secret lessons to secure the betrothal. They do not expect to fall in love.
Torn between his duty to complete his mission and his growing attraction to the princess, Diarmid walks a fine line between loyalty and betrayal. Can he keep himself away from her for the sake of the mission?