Michael Douglas thinks "courtesy" is the secret to a happy marriage

He said: "I think it just comes out of courtesy. You know, I think sometimes we take the person closest to us for granted. I would say sometimes we make more of an effort with strangers than we do with the person who's closest to us. And I've always tried to remember how fortunate I am and what an extraordinary lady she is and daily remember of that kind of respect."

And the 74-year-old actor thinks it is important to talk in relationships too.

Speaking to Us Weekly magazine, he shared: "It's taken me a long time but resentment is an easy thing to keep under the surface. I think most of the times it's really good to get things out sooner than later."

Meanwhile, Michael previously confessed his love for his wife Catherine "only continues to grow" and it knows no limits.

He explained: "We celebrated our 18th anniversary recently, and besides the genuine love that only continues to grow, I think the fact that we're in the same industry really helps us to understand what is going on. It was great for her to be here tonight and to share one of those nice things where your partner totally understands what's going on.

"I flashed back to the time when she was pregnant with our daughter in Chicago and for all the shows growing up."