Michael Douglas reveals why he refused to appear on David Letterman's talk show

Michael Douglas has finally revealed why he refused to appear on David Letterman's talk show for almost two decades.

In his new memoir One Helluva Ride, the Wall Street actor recounted how he had promoted various projects on the Late Show with David Letterman.

"I had been a regular guest on Letterman's show earlier in my career, but the last time I was on, I felt David went too far," he shared.

Douglas went on to recall how Letterman had played "without warning" a TV commercial that his actress mother, Diana Dill, had appeared in.

"(Letterman) started grilling me about it. It felt like he was making fun of my mother," the 82-year-old continued. "(That appearance) left me feeling like he had a real nasty sense of humour... After that, whenever the producers of the show requested to have me back on, I always refused. I said no for 18 straight years. Dave wrote me personal letters to apologise, but my feelings didn't change. He had crossed a line."

However, Douglas decided to "bury the hatchet" and announce that he was battling advanced tongue cancer during an interview on the Late Show with David Letterman while promoting his movie Wall Street: Money Never Sleeps in 2010. He has since recovered from the cancer after undergoing chemotherapy and radiation treatments.

"For years, my father (Kirk Douglas) and I had held on to grudges, used them to fuel our achievements, and looked to show people it was a mistake to cross a Douglas," he added. "But it felt so nice to clear the air with Dave, and for the first time I felt like life is too short to hold on to feuds. Letting go felt like it was more of a favour to myself than to Dave. Those grudges were a weight I carried, and I was done with revenge."

Letterman, 79, has not yet responded to the comments.

One Helluva Ride is now available.