change of heart

noun

1. a reversal of one's feelings, intentions, opinions, etc.:

   At first Mother said we couldn't go, but she had a change of heart and let us.

Word History and Origins

Origin of change of heart¹

First recorded in 1820–30

Idioms and Phrases

Altered feelings or attitude, as in Paul didn't like his new job, but a raise prompted a change of heart and he became quite enthusiastic . [Early 1800s]