The singer and actor made the revelation in her new memoir, Open Book, explaining she rejected the opportunity to play Allie, who was eventually portrayed by Rachel McAdams.
“I knew exactly what the movie was about because I had read the script,” she writes, adding she decided not to accept the part “because they wouldn’t budge on taking out the sex scene”.
She added: “And it would have been with Ryan Gosling, of all people.”
Simpson revealed Gosling was her first crush in the 1990s, when they auditioned for The Mickey Mouse Club together.
The Notebook, which told the story of a couple who fall in love in the 1940s, went on to become one of the most popular romantic dramas of the 2000s.
Elsewhere in her memoir, Simpson wrote that she was sexually abused as a child, and that it led to a dependence on drugs and alcohol as an adult.
“It would start with tickling my back and then go into things that were extremely uncomfortable,” she writes, in an extract published by People Magazine.
“For six years, I was abused by this girl during our family’s visits.”