My niece was "caught out" on Surprise Surprise.
My late sister in law arranged for the family (her, husband, son and two daughters) to go to the studio with the aim of surprising her husband - everyone being in on the joke except this eldest daughter who thought her father was going to get the surprise of his life.
Cilla came into the audience to speak to the family along the lines of "This is Pat Donley, with her husband etc.etc. but it's not your husband I have come to talk to and surprise, it is you Mandy!" The look on my niece's face was brilliant as she was totally gob-smacked.
Very clever how they set it up. She wanted to be a cheer leader, so they whipped her out of the audience and after a bit of training backstage with a semi-pro group from I think some London basketball team, she then came on at the end of the programme all kitted out in the same uniform and did a routine with them.
They all said what a lovely lady Cilla was.