Kaley Cuoco and Johnny Galecki
It was over before it was revealed. The Big Bang Theory costars secretly dated for two years in the first few seasons of their CBS comedy. In September 2010, Cuoco -- who married tennis pro Ryan Sweeting on New Year's Eve in 2013 -- opened up about the relationship for the first time in CBS Watch! Magazine. "It was a wonderful relationship, but we never spoke a word about it and never went anywhere together," she said. Galecki told the mag in December 2013 that the two were still friends. "Kaley's not just an ex, she's a part of my life."