Just last winter, Jimmy Kimmel and Sarah Silverman proved the strength of their comedic and romantic bond by making videos about—how to put this delicately?—courting other people. After premiering on Kimmel's late-night talk show Jimmy Kimmel Live! earlier this year, both Silverman's short film about her fictional fling with Matt Damon and Kimmel's retort proclaiming his affair with Ben Affleck became Internet sensations. Yet throughout the humorous one-upping, one thing was clear: "We really, really, really like each other," Silverman told PEOPLE in March. "He's kind and funny and maybe the most thoughtful person I know. Plus he feeds me and he tickles my back at night and he likes my unwanted hair." Kimmel was equally smitten. "Sarah is funny and smart and good to look at. Plus, she likes fat guys. What more could I ask?"

But neither Kimmel nor Silverman are joking about their relationship now. On July 14 reps for Kimmel, 40, and Silverman, 37, confirmed their breakup (first reported on Vanity Fair's Web site) to PEOPLE. "Jimmy and Sarah have and will have no further comment," they said in a joint statement. Sources say the split was mutual and there was no third party involved.

Kimmel and Silverman hit it off when they worked together in 2003 on Comedy Central's prank show Crank Yankers. "We kept talking at the same time, going for the same joke," recalled Silverman. "It kept happening all day. It was funny—and swoony. We're different in a lot of ways but also the same." The split came as a shock to many who saw the couple as rock solid. Just this past April, they celebrated Kimmel's episode 1,000 together.

Now the pair will have to focus on the funny in separate ways: She's shooting The Sarah Silverman Program, while Kimmel returned to his ABC show on July 14 after a two-week hiatus. "They're both back to work," says a source. "It's business as usual."