The Terminator star embarked on a relationship with the filmmaker in the early 1990s and the pair had a daughter together before marrying in 1997.
They split just eight months later when Cameron rekindled a previous relationship with Suzy Amis, who starred in his movie Titanic.
And Hamilton has a stark warning for the actress, who wed Cameron in 2000.
She tells Britain's Daily Mail newspaper, "The woman he can't get is always his dream girl.
"It's interesting because while he was making Titanic, Suzy at that time was the gargoyle on the end of my bed, waiting to swoop in.
"Now I'm the gargoyle on her bed because for Jim, the one who doesn't end up with him is always the one he wants. I'm the one who got away, and she has to live with that."
Cameron has been married five times - to Hamilton and Amis, as well as to Sharon Williams, Gale Anne Hurd and Kathryn Bigelow.