Alan Alda revealed he has Parkinson’s disease on Tuesday’s episode of “CBS This Morning.” The actor said he was diagnosed with the illness three and a half years ago.

“I’ve had a full life since then,” he said. “I’ve acted, I’ve given talks, I help at the Alda Center for Communicating Science at Stony Brook. I started this new podcast. And I noticed that — I had been on television a lot in the last couple of weeks talking about the new podcast — and I could see my thumb twitch in some shots and I thought, ‘It’s probably only a matter of time before somebody does a story about this from a sad point of view, but that’s not where I am.'”

Though he didn’t have any symptoms yet, Alda said, he asked for a scan after reading an article that said acting out your dreams could be an early sign of the illness. He noticed a twitch in his thumb months later.

“I want to know if there’s anything I can do, I wanted to do it before things start to show up,” he said. “The things I want folks to know, and this is not to shortchange people who are suffering with really severe symptoms, in the very beginning, to be immobilized by fear and think the worst thing has happened to you, it hasn’t happened to you.”

Alda, known for his roles in “M*A*S*H*,” “The Aviator,” “Tower Heist,” and “The West Wing,” shared that he’s still active. The 82-year-old takes boxing lessons three times a week and plays single tennis matches.

“Each day is different from the next… It’s like a puzzle to be solved. What do I have to adapt to, to carry on a normal life?,” he said. “I was mainly helping my family not be worried. It’s common for us all to go to the worst thought.”