The 80-year-old actor appeared on PEOPLE (the TV show!) where he spoke about Charlie's "recovery" from alcohol and drugs while promoting his new film 12 Mighty Orphans.
"I adore him," the actor said of his son. "I've always, always adored him. His recovery and his life is a miracle and he's an extraordinary man."
He continued, "We went through as you, as everyone knows I suppose, some very difficult times when he was out there. He's come back - thank heaven - and he's healthy and he's working on a book now."
Martin said Charlie, 55, was working on "an autobiography and he's very excited about that."
"He's very involved with his family, his children and grandchildren," Martin added.
Mark Sullivan/WireImage Father-son duo and actor Martin and Charlie Sheen
In 2016, Charlie opened up to Dr. Mehmet Oz about quitting drinking and drugs over the years, and his successful sobriety of 11 years until he relapsed after receiving his HIV diagnosis.
"It was to suffocate the anxiety and what my life was going to become with this condition and getting so numb I didn't think about it," Charlie said at the time. "It was the only tool I had at the time, so I believed that would quell a lot of that angst. A lot of that fear. And it only made it worse."
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Last year, the actor celebrated one year since he had quit smoking.
"Dear @my lungs," he wrote on Twitter. "It was one year ago TODAY, that I quit smoking ! hashtag - YOU'RE WELCOME !"
"If I could go back in time and have NEVER STARTED, I would absolutely do so," the actor added. "If you are on the fence about quitting, trust me; the sooner the better ! happy 4th !"
12 Mighty Orphans is now playing in select theaters.