Robert Downey Jr and wife swear by one crucial rule that's kept 18 year marriage going

Despite everything that's been thrown at them throughout their nearly two decades-long marriage, Robert Downey Jr and his wife Susan are still going strong.

They are one of the rare couples in Hollywood who have managed to weather the storms that being a celebrity brings with it, while also raising their kids and excelling in their careers.

At this point, the pair are basically the blueprint for a happy marriage.

Robert and Susan first met on the set of the 2003 horror film Gothika, when he was starring as a psychiatrist alongside Halle Berry and she was serving as a producer with production company Silver Pictures.

The filmmaker, 50, admitted she wasn't initially keen on the idea of dating a colleague, but the Iron Man star's quirky ways managed to charm the socks off of her.

"We were up in Montreal prepping for Gothika, and we had lunch with the director and Halle Berry," Susan previously told The Hollywood Reporter.

"Everybody else ordered Japanese, but Robert told us how oatmeal was the 'superfood'.

"He brought his own packets of oatmeal to have at lunch. And he had this box of various herbs and stuff. And then he started doing these yoga moves. I mean, he was interesting, but weird."

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Although most people would have no chance of scoring a date after doing the Downward Dog at lunch, Susan started seeing the Oscar-winning actor and they were quickly engaged by November 2003.

They then got hitched in a Jewish ceremony in Amagansett, New York, in August 2005 - and the rest, is history.

The couple have been married a whopping 18 years and now share two children, Exton, 12, and daughter Avri, nine, while also parenting Robert's son Indio, 30, who he shares with ex-wife Deborah Falconer.

And they even launched their own production company, Team Downey, which is behind the likes of The Judge, Dolittle and Sherlock Holmes 3.

But what is the secret ingredient to their long, successful marriage, I hear you cry?

Well, according to the pair, it's all about making time for one another and prioritising their family - as they refuse to be apart for more than 14 days at a time.

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During an interview with People, Susan explained: "We do have a two-week rule, which often feels too long, but we don't go more than two weeks without seeing each other and the family being together.

"Fortunately, we prefer to be a travelling circus when we can be."

Obviously they both understand that sometimes life can get in the way of this, especially in the line of work that she and her husband are in.

Suan continued: "I really admire and have a lot of empathy for couples who both have to be in front of the camera, because you get stuck and you have to make those choices.

"You keep the basic rule of two weeks, and then you don’t try and think too far ahead, because so much of what we do is oddly unpredictable. You just never know.

"Someone might get sick, or there might be a shutdown, or this or that. So you just have to have some basic things in place, and then you have to be willing to flow with the rest of it."

Robert then jokingly added: "It just gives me, honestly, something to attach my neurosis to that’s positive."

Here's to another 18 years, guys.