"I love Michael Douglas but he is misinformed," the 56-year-old Kiss Kiss Bang Bang star wrote in a lengthy post. "The last time I spoke to him was almost two years ago, when I asked him for a referral for a specialist to get a diagnosis for a lump in my throat."
"I ended up using a team at UCLA and have no cancer whatsoever," he continued. "I still have a swollen tongue and am rehabbing steadily."
During a Q&A with Jonathan Ross at the Theatre Royal Drury Lane in London, England, on Sunday, Douglas told the crowd that Kilmer had been diagnosed with tongue cancer just like he had been in 2010.
"Val was a wonderful guy who is dealing with exactly what I had, and things don’t look to good for him,” Douglas, 72, said of his former Ghost and the Darkness co-star. “My prayers are with him. That’s why you haven’t heard too much from Val lately."
While Kilmer categorically denies having cancer, he said he also harbor's no ill will toward the celebrated actor, writing, "Whatever led Michael Douglas to speculate about my health, he's a loving and devoted friend to a privileged group of talent people around the world, and I'm sure he meant no harm."
Kilmer, an outspoken and life-long Christian Scientist, went on to say that some of his fans have "mistakenly thought my silence about my personal issues meant that somehow I wasn't being responsible to my health, because of my reliance on prayer and Love."
"Nothing could be further from the truth," he wrote. "I hope this puts to rest any further concerns about my health."
The actor, who most recently starred in 2014's Tom Sawyer & Huckleberry Finn in which he played author Mark Twain, said he is "very grateful for all the support from around the world."
"Being healthy and having the respect of my peers and love from my family, friends, peers and fans is a DAILY source of inspiration, for which I am so grateful, you have no idea," he concluded. "I work VERY hard at my craft, and being appreciated since I was a little boy for being able to give this gift, has literally made my life."
After Douglas commented on Kilmer's health, a source close to Douglas told ET that while the actor did speak about Kilmer's alleged cancer, he also "hasn't heard from Val in a long time," adding, "I don't think Michael's heard from him in over a year." Check out the video below to hear more.