Lisa Robin Kelly, an actress best known for her long-running role as Laurie Forman on "That '70s Show," died at age 43 on Wednesday.

Kelly had been staying at a rehab facility in California when she passed away in her sleep, according to TMZ.

Kelly's agent told the gossip site that the actress had voluntarily checked herself into treatment during the past week.

 'That 70's Show' star Lisa Robin Kelly after an arrest for assault. The actress died in her sleep at a California rehab facility at the age of 43.

"I spoke to her on Monday and she was hopeful and confident, looking forward to putting this part of her life behind her," Kelly's agent, Craig Wyckoff, told People. "Last night she lost the battle. Cause of death has not been issued yet and no death certificate has been issued either." 

Connecticut-born Kelly debuted in an episode of "Married..with Children" in 1992. She also appeared on television shows "Murphy Brown" and "Charmed," as well as TV movie "Amity Dollhouse."  Kelly's best known part was on "That '70s Show," on which she played the older sister of Topher Grace's character Eric Forman. When she left "the FOX sitcom after five years, she was replaced by actrss Christina Moore. 

In an interview with ABC News, Kelly opened up about her struggles with substance abuse after she left the show.

"I had lost a baby," Kelly said. "As a result of that I lost it. I lost everything and I was abusing alcohol."

"With 'That '70s Show' I was guilty of a drinking problem, and I ran," she added.

Kelly had been arrested several times in the past three years for a string of incidents. In 2010, Kelly pled guilty to misdemeanour drunk driving, earning her a night in jail and a year of unsupervised probation. In March 2012, Kelly was arrested on a count of spousal abuse, though charges were later dropped. In November of the same year, Kelly and her husband Gilliam were both arrested for assault. In June of this year, the actress was arrested again on suspicion of driving under the influence. 

In June Kelly had filed for divorce from Gilliam, citing irreconcilable differences for as the cause of their split.