When we had a surprise party for my Dad's 80th his elderly friend phoned him that morning to say that he was unwell and couldn't come. We sort of laughed it off and thought we'd covered it up but after the meal Dad stood up with a long speech and poem he'd prepared. Seems like he'd had an inkling anyway but it was a great success and a happy time. I'm sure the OP's party will be much enjoyed by all too.
Is there such a thing as delicious ready meals?