It’s no secret that the producers of American Idol like to keep the names of performers on finale night under wraps.

But two things are certain — Crystal Bowersox or Lee DeWyze will be crowned the season 9 champ on Wednesday, and fans will see the last of Simon Cowell before he jumps over to X Factor in 2011.
But a source tells PEOPLE that a special send-off planned for the cranky judge will feature some Idol alums, including a special appearance by Paula Abdul.

And among the superstars taking the stage? Watch for a great performance by Christina Aguilera.