'Cheers' Star John Ratzenberger SHOCKED By Danny Devito / Rhea Perlman Split

Danny DeVito and Rhea Perlman's split didn't just come as a surprise to their fans ... it also blindsided their close friends -- including "Cheers" actor John Ratzenberger, who claims he had NO IDEA the famed couple was calling it quits.

Ratzenberger -- who played Cliff on the 80s sitcom alongside Rhea -- said he just saw his old co-star the other day and she didn't even suggest things were going south with her husband of 30 years.