The phrase "实不相瞒" is formed through the sequential combination of four characters: the adverb "实" meaning "actually" establishes factual emphasis, followed by the negative particle "不" meaning "not", which then modifies the reciprocal prefix "相" meaning "mutually", and finally the verb "瞒" meaning "to conceal", resulting in a literal construction that means "actually not hiding from each other", which serves as a fixed expression used to introduce a candid remark.