It's a tale as old as time: good girl falls for bad boy; good girl ends up broken-hearted because the bad boy wouldn’t change his ways.

In this version of the classic, the good girl was Sarah Jessica Parker and the bad boy was Robert Downey Jr.

The pair met on the set of their 1984 teen thriller,Firstborn, in Los Angeles. He was an up-and-coming actor with naughty heartthrob vibes, while she was a theatre girlie, fresh off the plane from New York.

From the outside, they seemed an unlikely pair – and behind closed doors, their connection was even more baffling.

They seemed to be polar opposites, yet they stuck it out for more than seven years.

They were 12 months into their relationship when it became apparent that Downey Jr had serious substance abuse issues – something Parker has opened up about in a new interview with The New Yorker, saying that the situation "made her feel like a parent at the age of 22".

“People around him would be dismissive of me, but I had given him stability and tried to create a steady heartbeat that allowed him to show up on time,” SJP told the publication.

“That made me angry and embarrassed me.”

Watch: If alcohol was a person, she'd be wreaking havoc everywhere. Post continues after video.

Parker never went down the path of alcohol and drugs as her then-boyfriend. In fact, she didn’t do drugs and barely drank, she told writer Rachel Syme. “She told me that she never felt it 'necessary' to have a rebellious phase of any kind," Syme shared in the piece.

They were both just 18 when they started dating, but by 1991, when Parker was 25, she ended the dysfunctional relationship and went back to New York. There, she went on to date the late John F. Kennedy Jr, and married actor Matthew Broderick in 1997.

But it took her seven years to end the relationship with Downey Jr – and she explained why on the podcast WTF With Marc Maron.

“You love this person, and you’re afraid they’re going to die if you aren’t there to shore up their base every single solitary day," she said. "I just didn’t want him to die.

But she finally did, saying, “Eventually, I guess I just summoned the courage to leave him."

At the time, her decision was gut-wrenching – but looking back, she knows her decision was a brave one.

"The biggest, hardest choices about those kinds of relationships are feeling brave enough to leave, even if you think they’re going to die."