Spill the Beans(reveal a secret)
Did you know that Harry was going to take Kathy on a Caribbean cruise?
Yes, I did. He was planning on surprising her with the tickets for their anniversary, but someone spilled the beans.
What a shame! That was supposed to have been a surprise.
Yes, it's too bad that someone told her about the trip beforehand and ruined Harry's surprise.
That's OK. Her enthusiasm was not dampened in the least!
was supposed to = 〜する手筈であった
not in the least = まったく〜でない、ちっとも〜でない
dampen = （気持ちを）くじく
cf. get beans = しかられる use one's bean = 頭を使う