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).
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.”