Article continues below advertisementTrey Parker and Matt Stone rarely sit down for interviews together. That's part of why their upcoming appearance on The Late Show with Stephen Colbert is drawing unusual attention across the entertainment world.The South Park creators will join Stephen Colbert on the March 16 episode of the CBS late-night show to mark the 15th anniversary of their Tony Award-winning Broadway musical The Book of Mormon. The episode will also feature original cast stars Andrew Rannells and Josh Gad, along with a performance from the current Broadway cast.