Catherine Zeta-Jones and Michael Douglas Share the Secret to Their 17-Year Marriage (Exclusive)

"It's been a great 17 years."

After 17 years of marriage, Catherine Zeta-Jones and Michael Douglas haven't lost the love.

On Thursday night, the Hollywood power couple happily posed together at a screening for the 48-year-old actress' upcoming Lifetime movie, Cocaine Godmother, The Griselda Blanco Story, in New York City. Zeta-Jones rocked a chic black jumpsuit that matched Douglas' all-black ensemble.

Upon chatting with Zeta-Jones, ET had to know the couple's secret to being married for nearly 20 years. "I think understanding, listening, being friends, all helps," she shared. "It's been a great 17 years."

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In Cocaine Grandmother, Zeta-Jones takes on the real-life role of drug lord Griselda Blanco, who was a pioneer in the Miami-based cocaine trade. Upon taking on such a challenging part, the Tony winner admitted that she got some advice from Douglas, a two-time Oscar-winning actor.

"He did say to me, which I took with me throughout the whole thing [and] which was a little disconcerting, 'Honey, remember when you do nothing, you are your most scariest,'" she said. "So, I went, 'Alright now, OK. So,17 years on, it's like when I do nothing, I scare the crap out of him!"

She quipped, "That's a good lesson. ...He did tell me that and I did take that with me. ...I guess I am pretty scary."

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ET also spoke with Douglas, who admitted that he was a little scared of his wife when she was in character. "There were a few times and a few days [when] she gave us that look, that look of the cocaine godmother," the 73-year-old actor recalled. "She left it mostly up there in front of the camera but in the prep, I'd say, 'Honey, easy, easy.'"

Douglas went on to share why he thinks he and Zeta-Jones have such a successful marriage. "I think mutual respect," he said. "I admire Catherine so much and in so many ways -- as a mother, as an actress, and now as a business woman."

It's clear Douglas is a proud husband as he couldn't stop gushing over his wife's intense role in Cocaine Grandmother, which airs Jan. 20 on Lifetime.

"I'm so proud of her," he said in praise of Zeta-Jones. "[It's a] great role for her and she just kills it. She had a lot of fun doing it -- serious acting. I don't know where it came from!"

The pair have had some ups and downs in their marriage -- including when they briefly separated in 2013 -- but in an exclusive interview with ET in January 2016, Douglas said that the highlight of his life in the entertainment industry was when he was introduced to Zeta-Jones. 

"Right now, it would probably be the Deauville Film Festival in 1999 when I met Catherine," he raved. "That was the best memory I got."