"Vampire Diaries" stars Nina Dobrev and Ian Somerhalder have reportedly broken up.

Somerhalder tweeted a sober quote from playwright Lillian Hellman: "A thought for today: 'People change and forget to tell each other,'" Somerhalder shared with his 3.6 million Twitter followers.

A source assured Us Weekly that the pair's split will not affect their behavior on the set of "Vampire Diaries," which is in its fourth season and in February was renewed for a fifth season. Somerhalder and Dobrev are professionals who "will continue to work together and remain best friends, which is where the relationship started," the source said.

Nina, 24, and Ian, 34, had a rather private relationship and kept out of the media's eye. Nina gave a rare look into her relationship last September in an interview with Seventeen magazine.

"I didn't want to be dating one of my costars," the actress said. "My goal on the show was to be professional. But sometimes you can't help who you have a connection with, and you can only fight it for so long - which I did for a really, really long time."

The couple met on their CW set in 2009 and started dating the next year. They went public with their relationship in 2011, Life & Style magazine reported.