In the days before her tragic death in 2012, Whitney Houston made a promise to Clive Davis -- to quit smoking.

Although the singer claimed to have quit taking drugs, she admitted she still harbored a nicotine addiction.

"We were trying to get her to stop smoking," Davis tells Playboy, reports. "It was a serious problem because it affected her singing. She would say, 'I kicked the drug habit, but this is more difficult.' She had cut back on cigarettes, but the week she died she came to my bungalow and said, 'I understand I can't just cut back. I've got to stop. I promise I will.'"

Ultimately, it was Houston's drug problem that contributed to her untimely death

"I only became aware of any problem in maybe the mid-1990s," the record exec says. "I didn't know she was in trouble. I didn't know how bad her problem was. It was after a Michael Jackson concert at Madison Square Garden in the late 1990s when I knew [for sure]. She showed up ghastly thin. I met with her."

Davis believes that for a period of time, at least, the "I Will Always Love You" singer managed to stay sober.

"We talked about the drugs she was using," Davis added. "I tried to help her. I tried to work with the family to help her. She did better for a long time, at least as far as I knew."

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