Matthew Perry was "happy and chipper" when Friends co-creator Marta Kauffman spoke to him two weeks ago, she says.
Perry, who played Chandler in the TV sitcom, died on Saturday aged 54.
Kauffman told NBC's Today programme their last chat had been "great", adding: "He was in a really good place, which is why this seems so unfair."
Perry had battled addictions to alcohol and drugs for most of his life, but Kauffman said: "He wanted to help other addicts and it gave him purpose."
The actor was found dead in a hot tub at his Los Angeles home.
A post-mortem examination was inconclusive and officials are awaiting the results of toxicology tests.
Friends co-creator David Crane said helping other addicts "absolutely became his purpose his reason for being".
He turned his $10m Malibu beach compound into Perry House, a men's sober living facility, in 2012, and the project received an award from the White House the following year.
He sold it two years later but said he was still committed to providing services for recovering addicts.