Idiom 8: RIGHT/STRAIGHT FROM THE HORSE’S MOUTH
Meaning: If you get news or other information “right/straight from the horse’s mouth”, you get it straight from the source, that is, from the person or people who know most about it (usually because they are directly involved).
Examples:
A: “Are you sure Harry’s getting married?”
B: “Yes! I got it straight from the horse’s mouth. Harry phoned me the other day to tell me.”
A: “There’s a rumour going round that this will be the last season of “Game of Thrones”.
B: “Really? Well, I won’t believe it unless I hear it right from the horse’s mouth.”