I'm the Villainess, So I'm Taming the Final Boss, Vol. 3 LN

After being assaulted, Demon Lord Claude loses his memories, his powers, and even
forgets his engagement with Aileen! Soon, Lilia begins courting him once again, and
this time Claude seems to be falling for it hook, line, and sinker. The Bad End Aileen
thought she-d avoided is back with a vengeance!