"Unfortunately, Lisa Robin Kelly passed away last evening," Craig Wyckoff told People.com Thursday.
"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," Wyckoff said.
"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. Cause of death has not been issued yet and no death certificate has been issued either."
Wyckoff said Kelly died in her sleep.
2014: The Year in Music [PHOTOS]