Is expiation obligatory for one who reveals a secret when its owner requested that it not be revealed by saying, "Don't tell anyone," or "It's a trust"?

It is forbidden to disclose a secret that the informant commands to be kept, and it is unlawful for every accountable person to spread or publicize what is meant to be concealed, especially if he was ordered to keep it secret, or if a clue indicated its confidentiality, or if it is customarily kept secret. For gatherings are by trust [Al-Majālis bi-l-amāna], and if a man tells another a narration and then looks around, it is a trust. And whoever hears a narration that he dislikes being mentioned about him, it is a trust. There is no specific expiation required for disclosing a secret; rather, repentance to Allah Almighty is obligatory for this sin.