“I looked over at Harrison. A hero’s face — a few strands of hair fell over his noble, slightly furrowed brow,” she writes. “How could you ask such a shining specimen of a man to be satisfied with the likes of me?”

Although their unlikely romance took Fisher by complete surprise and ran its course once the film wrapped, she remembers the time fondly.

“I was so inexperienced, but I trusted something about him,” she says. “He was kind.”

For much more from Fisher — and to read the exclusive excerpt of The Princess Diarist — pick up this week’s issue of PEOPLE, on newsstands Friday.

Carrie Fisher is finally going public with a secret she has guarded closely for 40 years: When she was 19, she and Harrison Ford, then a 33-year-old married father of two, had a whirlwind three-month affair while filming the original Star Wars in 1976.