Douglas discussed his battle with throat cancer during an interview on friend Alec Baldwin's WNYC radio programme.
The Wall Street: Money Never Sleeps star admitted that he was totally overwhelmed when a doctor told him he had a late-stage form of the disease.
"I'll never forget that moment when [the doctor] looked up at me and looked back down. I knew, and he said, 'Well, I guess we're going to have to take a biopsy, see there's a polyp here', it was on my tongue. Two days later, he called me back and said, 'You've got cancer'," Douglas revealed.
The actor said that he only discovered the diagnosis by accident after suffering some slight pain in his mouth, which he initially blamed on the stress of playing Wall Street's corrupt financier Gordon Gekko again.
"I thought maybe [the pain] was from tension, from the part, where you haven't placed your voice, where you're swallowing your words and you speak from the back of your throat," he said. "I had a little bit of a sore gum and so I saw doctors."
In January, Douglas announced that he had beaten cancer after undergoing extensive treatment for several months.
Douglas has cautioned others to see a doctor immediately if they notice anything out of the ordinary on their own bodies.
He commented: "The thing with cancer is that you want to get it as early as you can."
Douglas will star in director Steven Soderbergh's action film Haywire, which opens on January 20, 2012 in US and UK cinemas.
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Watch a trailer for Haywire below: