Catherine Zeta-Jones has revealed “being friends” with her husband Michael Douglas has helped their romance stay on track

Asked what the secret to their marriage is, the ‘Chicago’ star said: "I think understanding, listening, being friends, all helps. It’s been a great 17 years.”

Michael, 73, on the other hand, believes the key to their lasting romance is the “mutual respect” they have for one another.

When asked the same question, he said: "I think mutual respect. I admire Catherine so much and in so many ways - as a mother, as an actress, and now as a business woman.”

The pair met in 1998 and became engaged a year later, before tying the know in 2000.

Their romance hasn’t always been smooth sailing though, as they decided to live separately for a brief time in 2013, but did not take the legal action necessary to start a divorce.

However, after reconciling in 2014, they are still going strong, and Catherine recently took to Instagram to celebrate their 17th wedding anniversary, which they marked in November.

Alongside a picture of the pair on their wedding day, Catherine wrote on the photo sharing app: "17 years ago today, I said 'I do' to my best friend and father of our two and a half month old son. Thought it could never get better than that day, but it did. Happy anniversary darling, Michael. With you, in my life, and Dylan and Carys, every day could be a twelve hour fantastic party at the Plaza in New York. Love you. #love #lovestrong (sic)"