We want to give him a surprise, so please keep quiet about the birthday party.

我们想给他一个惊喜，所以请对生日派对这件事情保密。

youdao

We made a special arrangement for mother's birthday party, which will definitely be a surprise.

我们为妈妈的生日聚会做了特别的安排，这一定会是个惊喜。

youdao

I bought a nice wrist watch as a surprise for my wife's birthday.

我给我太太买了一只很好的手表作为生日礼。

youdao

The business card idea makes Schacht wonder whether the tiny balls might be added to a birthday card to reveal a surprise message when the card is held over birthday-cake candles.

FORBES: Magazine Article

Now, if truth be told, I really don't want the government to know if I am planning a surprise birthday party.

BBC: E-mail: Who's reading yours?

The birthday trip was a surprise.

BBC: Down Hall pool deaths: Drowned couple 'on surprise break'