Danny DeVito, left, and Charlie Day, photographed at Fox Studios in Los Angeles this month, are back for Season 17 of "It's Always Sunny in Philadelphia," which turns 20 this year.

Rob McElhenney, Glenn Howerton, Kaitlin Olson, Danny DeVito and Charlie Day act during a dance scene on the set of “It’s Always Sunny In Philadelphia” on May 23, 2007.

Danny DeVito: ‘It’s Always Sunny in Philadelphia’ Is Like ‘I Love Lucy’ on ‘Acid’ "You could do anything you wanted," DeVito said of starring in 17 seasons of the hit FX comedy series.

Danny DeVito, left, and Charlie Day, photographed at Fox Studios in Los Angeles this month, are back for Season 17 of "It's Always Sunny in Philadelphia," which turns 20 this year.