This is the 8779th most frequent Japanese word.
本当は
"Actually; in reality; the truth is."
本当は conveys the curiosity or ambiguity about someone's real nature or character.
彼が本当はどんな人なのか分からない。
I don't know what kind of person he really is.
本当は is used here to signify the speaker’s true feelings or reality, contrasting with what might have been assumed or appeared.
本当は彼が好きじゃなかったです。
Actually, I didn't like him.
本当は is employed to express a truth or honest admission regarding the speaker's desires or intentions.