Lisa Robin Kelly who played Eric Foreman's (Topher Grace) older sister Laurie on "That '70s Show" was found dead after suffering an apparent cardiac arrest in her sleep at a rehab facility in California.

Kelly's agent told TMZ that the actress had just voluntarily checked herself in for treatment for an alcohol problem this past week ... and was determined to clean herself up.

The agent added that, "She had been fighting demons for a while and finally lost her battle."

Lisa had been in and out of rehab centers hoping to kick her alcohol problem ... and most recently fell off the wagon after a huge dispute with her estranged husband Robert Gilliam.

Kelly's estranged husband allegedly beat her last May to obtain residual money from her show. He was convicted of domestic battery last month and sentenced to 3 years probation. He also served 35 days in jail for the beating.

Lisa filed for divorce from Gilliam back in July.

According to the TMZ article Lisa's new boyfriend brought her to rehab again on Monday ... but she went into cardiac arrest late Wednesday night and could not be saved.

The boyfriend blames her estranged husband for the relapse.