The 32-year-old singer finally admitted as much Thursday on Watch What Happens Live. Clarkson and Guarini met as contestants on season one of American Idol in 2002, and co-starred in From Justin to Kelly in 2003.
"We didn't date during Idol, which everybody thought we were dating," she revealed to host Andy Cohen. "I feel like we weren't dating during the movie. But I feel like maybe we did."