“That 70s Show” star Lisa Robin Kelly died at the age of 43 on Wednesday. The actress had struggled with substance abuse, and according to TMZ, the blonde beauty checked herself into a rehab facility a week ago.

Fans of “That 70s Show” and Kelly took to Twitter early Wednesday evening to share their condolences and mourn her tragic passing. Check out their tweets below:

"That 70s Show" co-stars Topher Grace, Mila Kunis, Laura Prepon, Wilmer Valderama, Danny Masterson and Ashton Kutcher have yet to publicly comment on Kelly's passing. Her agent, however, issued a statement:

"Unfortunately Lisa Robin Kelly passed away last evening," her agent Craig Wyckoff told E! News. "Lisa had voluntarily checked herself into a treatment facility early this week where she was battling the addiction problems that have plagued her these past few years. I spoke to her on Monday and she was hopeful and confident, looking forward to putting this part of her life behind her. Last night she lost the battle."

He added: "Cause of death has not been issued yet and no death certificate has been issued either."

Kelly was once best known for playing Laurie Foreman, but in recent years she began to make unwanted headlines for recurring battles with drugs and domestic disputes with husband Robert Gilliam.

In 2003, Christina Moore replaced her on “That 70s Show,” and a few years later her legal troubles began to play out in the media. In April 2012, Kelly was arrested for domestic abuse, and then once more in November 2012 for assault after another fight with her husband in their New Orleans home. Most recently she was arrested for DUI on June 22.

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