By DAILY MAIL REPORTER and CAROLYN HIBLEN
Lisa Robin Kelly has died aged 43 at a Californian rehab facility, it has been confirmed.
The That '70 Show actress is believed to have suffered a cardiac arrest and passed away on Wednesday after attempts to revive her failed.
Lisa, who endured a long struggle with alcohol addiction, checked herself into a treatment centre on Monday determined to clean herself up, according to her agent.
Her spokesman confirmed to TMZ on Thursday: 'She had been fighting demons for a while and finally lost her battle.'
Lisa was brought to the rehab facility by her new boyfriend on Monday, the website reported.
But just two days later, emergency responders were called when the actress was found unresponsive with needle marks on both arms.
Her new boyfriend - whose identity is not known - claimed the needle marks were not drug-related but were caused by multiple attempts to draw blood after she was hospitalised on Sunday with a blood alcohol level of .34, TMZ reports.
Lisa's manager, Craig Wyckoff, told FOX411 he had spoken with the troubled star on Monday and she was 'hopeful and confident, looking forward to putting this part of her life behind her'.
Lisa is seen here in her mugshot after being arrested for drunk driving in Mecklenburg County, North Carolina in December 2010
He also confirmed that she had voluntarily checked herself into the centre after being in and out of treatment facilities for alcohol addiction - she vehemently denied taking drugs - trying to get on the road to recovery.
She is reported to have fallen off the wagon following a huge dispute with her estranged husband, Robert Gilliam.
'She was battling the addiction problems that have plagued her these past few years,' Wyckoff said, adding, 'Cause of death has not been issued yet and no death certificate has been issued either.'
Lisa starred alongside Ashton Kutcher in That '70s Show, though while he went on to bigger and better things, she virtually disappeared from the limelight after leaving the show
Tributes are slowing starting to come in for the actress as the tragedy reaches friends and co-stars.
Danny Masterson, who played Steven Hyde in That '70s Show, was the first to send his love after a fan tagged him and his co-stars in their tweet.
'Terrible, awful news. Brilliant on 70s.... See u next time LRK,kisses,' he tweeted.
Dennis Haskins, who played Mr Belding in 1980's hit TV show Saved By The Bell, also took to Twitter to express his thoughts.
He wrote: 'I'm sad to hear that Lisa Robin Kelly lost her battle while in rehab fighting to live. #RIP.'
Lisa posted this glamorous pic to her Twitter account in September 2011, before her personal demons took hold
Meanwhile, a close friend known only as Nik has taken to the late star's Facebook page to post a message to fans.
'Lisa is gone and that's hard to digest,' they wrote. 'On her behalf I want to thank everyone for all their supportive emails and just know she was aware and grateful for each of you.
'If more people were supportive like you guys, she'd be alive today.
'She was a beautiful soul and a real artist... and I will never forget her.'
The actress had been on a tragic downward spiral in recent years, arrested at least four times in the last three years - for DUI, spousal abuse and assault.