Yuusha ni Uragirareta Tensei Chiyuushi ga Maou no Chouki ni Naru Made

Alicia, who was reincarnated into a different world and raised there as an orphan, had been engaged to her childhood friend Chris. But after becoming the Hero, Chris falls in love with the saintly Princess Irene at first sight. Then giving into the princess's temptation, he ends up stabbing Alicia. Alicia is both literally and figuratively brokenhearted by this betrayal, but who should come to save her but the Demon King himself, even though she had always thought of him as the enemy...