As promised, CBS today announced the surprise twist at the center of Big Brother 4 (debuting July 8 at 8 pm/ET): Some of the housemates will be stunned to discover that they're competing against ex loves. "No reality show has ever done what we're about to do," says exec producer Arnold Shapiro. "The result is unpredictable. The only certainty is that everyone involved will be shocked and will likely have to re-think their strategy." Truthfully, that's not the only certainty. For example, I know for a fact I won't be watching.