expression
to tell the truth; actually; in reality
Fixed expression used as a sentence opener to introduce a candid or honest statement, often when admitting something or revealing true feelings.
実のことを言うと、彼のことはあまり好きじゃない。
To tell the truth, I don't really like him.
実のことを言うと、まだ準備ができていないんだ。
Actually, I'm not ready yet.
Phrase composed of 実 (truth/reality), の (possessive particle), こと (abstract thing), を (object marker), 言う (to say), and と (conditional/quotative). Literally 'if I say the real thing', it became a set expression meaning 'to tell the truth'.