Lots of good advice here, hope it’s helpful. But I don’t think I have EVER been to a surprise party that was a real surprise for the surprisee!
Although on reflection, there was one surprise hen night I went to, and the bride-to-be was an hour late as she had popped to the shops first and also a bit annoyed that her fiancée had been keeping the surprise from her!
Another friend’s husband arranged a surprise 50th party for her, and when asked if she had known in advance, said of course she did, how did anyone think that the house would have been so tidy and organised, with enough food, drink, etc, to go round?
I would let it go, your husbands friend was not being malicious, and I think that most people would like a bit of warning so that they can prepare themselves mentally AND get their very ‘surprised’ speech ready!
Hope it goes well, do let us know what happens, please. ???