EXCLUSIVE: Spencer Tracy and Katharine Hepburn — The Real Story of Their Rocky Romance

There's a famous story about the first time Katharine Hepburn met Spencer Tracy, RadarOnline.com can reveal.

The Oscar-winning actors were set to star together in 1942's Woman of the Year, TCM host Ben Mankiewicz told said: "My great-uncle, [producer] Joe Mankiewicz, introduced them. And Katharine says, 'I'm afraid, Mr. Tracy, I'm a little too tall for you.' And then Joe says, 'Don't worry, Kat, he'll cut you down to size.'"

That turned out to be true. At the time, Hepburn was at the top of her game, coming off of The Philadelphia Story. She was also known for having "pure determination and sheer force of will," said her nephew Mundy Hepburn.

But when Kate met Tracy, as she called him, and embarked on a 27-year love affair with the married actor, it changed her.

"I loved Spencer Tracy," she wrote in her memoir, Me: Stories of My Life. "He and his interests and his demands came first."

Even though he refused to leave his wife, and despite his alcoholism, Katharine stood by her man.

"The relationship between them was fascinating. They were kindred spirits," Christopher Andersen, author of An Affair to Remember, said, marveling that they kept it secret for so long despite the fact that they were so famous.

Katharine had already dated famous men, including Howard Hughes, when at 34 she met Tracy, 41. She found him irresistible and called him "the perfect actor," but he also made her laugh. Mankiewicz credits her with broadening Tracy's career.

"She exposed his ability to do comedy," he said, as can be seen in many of their nine films together.

Tracy, however, was an alcoholic. And he'd been married to actress Louise Treadwell, with whom he had two children, since 1923. He refused to divorce. "He felt guilty because he had a deaf son," said Andersen. "He also didn't want to put his wife through scandal."

So he and Kate "had to sneak around," added Andersen. He would spend weekends with his family and the weeknights with Katharine. "He would come back on a Sunday and Kate would have dinner ready for him."

She was devoted to his happiness. "When they were around other people, she sat at his feet and worshipped him," said Andersen. Still, "on the big issues," such as her wanting to go film The African Queen in Congo, Kate stood firm.

And they fought.

"They had pitched battles," Andersen noted. When Tracy drank, "he threw chairs through restaurant windows."

Katharine admitted that he even hit her "once" in a drunken stupor.

She thought about AA, she said, but worried it would destroy his career if news got out. And she refused to leave him – if she had, she later shared, they both would have been miserable.

That belief kept her by Tracy's side until his death from a heart attack 17 days after they finished filming 1967's Guess Who's Coming to Dinner. Even years later, Katharine, who died in 2003, insisted she had no regrets.

"Love has nothing to do with what you are expecting to get – only what you are expecting to give," she said, "which is everything."