to be honest
spoken used when you tell someone what you really think:
口语,用于你要告诉某人你的真实想法
To be honest,I don't like him very much.
Honestly
spoken used when you are shocked or annoyed by something someone has said or done [= really]:
口语,用于当你被某人的话或其所做的事震惊或者烦恼
Honestly!Do you ever listen?