Michael Douglas, 79, makes very NSFW relationship admission about marriage with Catherine Zeta-Jones

Whilst the majority of big-name stars prefer to remain rather tight-lipped about their intimate antics, Michael Douglas is, apparently, spreading the word.

In fact, just this week, the 79-year-old made an unexpected confession about a rather x-rated punishment wife Catherine Zeta-Jones forces onto him when he loses out to her during a round of golf.

The duo are avid golfers. (Ross Kinnaird/Getty Images)

Despite fans initially shocked when the celebrity power went public with their relationship back in the 90s - due to the actors' staggering quarter-of-a-century age gap - their partnership has seemingly gone from strength to strength.

Proving age is just a number, over the last 25 years since they the loved-up duo tied the knot in a plush New York City ceremony at exclusive Plaza hotel, the pair have gone on to welcome two children together.

And in numerous occasions when catching up with press ever since, Douglas and Catherine have given fans a glimpse into what makes their relationship so special.

The Basic Instinct actor famously once said: "True love takes work. Love is an extraordinary feeling that comes from the bottom of your soul, but has to be nurtured, you know.

"The thing I’ve learned about getting older is you can’t take love for granted. You protect it, nurture it, and it grows, and after one’s initial, physical, emotional aspects, it becomes deeper."

The couple are more loved-up now than ever. (Axelle/Bauer-Griffin/FilmMagic)

And this week, as we say, Michael has this week lifted the lid on the ways in which he and his wife, 54, keep one another on their toes.

Speaking to television personality Alyssa Farah Griffin this week, the actor was heard reflecting on the couple's interest in playing golf together.

Asked about what happens if his Swansea-born wife takes the victory, he left the interviewee utterly blindsided when revealing how she punishes him.

"What does she make you do when you lose to her?" the presenter asked.

And - without skipping a beat - the New Jersey star replied: "Whip it out."

Michael then went on to elaborate: "'[She says] 'You’ve got to whip it out. Drop the trou and whip it out.'"

A visibly shellshocked Alyssa then teased in response, 'That’s the secret to a marriage,' to which Michael jestingly replied: "I’m going to be 80 in September, so now I play off of ladies tees, too, so I don’t have to do that anymore."

Michael and Catherine are parents to 23-year-old son Dylan and 19-year-old daughter Carys, with the actor also fathering now 45-year-old actor Cameron Douglas, from his first marriage to Diandra Luker.