"RIP Connie," Sullivan tweeted Monday. "It was a great two years! Thank you for your love and support, it means so much. Long live GH!"
It was a particularly tumultuous two years for the Brooklyn-born Connie, who had reinvented herself as the stylish fashion magazine editor Kate.
Connie/Kate was killed apparently by a man whose life she turned upside-down with an expose she printed in her magazine's sister newspaper.
She also almost lost her fashion magazine and her gangster fiance Sonny in recent months after successfully conquering her dissociative identity disorder -- for which she developed an alternate personality. She also had to deal with the long-lost son she thought was dead for the last 20 years, who she then accidentally killed by running his car off the road.
The role of Kate/Connie was originated by actress Megan Ward, who played the character from 2007 to 2010. Sullivan took over the part in 2011.
Although Sullivan didn't say why she left "GH," she has several film projects lined up.