Researchers have used digital technology to scan a few specific pages of Anne's diary which had mysterious brown masking paper glued onto them.
The museum that houses the original, hand-written manuscripts that became The Diary of a Young Girl decided in 2016 to examine what was under two pages that were covered with "brown gummed paper".
Frank van Vree, director of NIOD: "Anyone who reads the passages that have now been discovered will be unable to suppress a smile".
While experts don't know why she covered up the four jokes and 33 lines about sex education, Frank mentions in her diary concern that others might read her personal thoughts. "As mattresses for the soldiers".
Writing about prostitution, she said: "All men, if they are normal, go with women, women like that accost them on the street and then they go together".
On the first new page, Anne Frank crossed out some words in such a way that they are no longer readable. "Papa has been there".
The two pages were dated September 28, 1942, when Anne would have been 13, less than three months after she, her family and another Jewish family went into hiding from the Nazis in a secret annex in a house in Amsterdam.
The Anne Frank House alongside Huygens Institute for the History of the Netherlands presented the diary findings at a press conference this week.
The BBC reports that the pages also contain Anne's musings on giving "the talk" to someone else, and reveal that her father had told her what prostitutes were. "Anne Frank writes about sexuality in a disarming way", Ronald Leopold, executive director of the Anne Frank House, said in a statement shared on the website. He added that Anne Frank's father, Otto Frank, already published texts that she would rather not have made public. The first was written in a series of small notebooks, from her 13th birthday on June 12, 1942, until August 1, 1944, and was intended strictly for herself.
The Lynn Classical High School Drama Club will perform "The Diary of Anne Frank" on Friday, May 18 and Saturday the 19th at 6 p.m. Tickets are $5. The dirty jokes are classics among growing children. The passages show how she "creates a fictional situation that makes it easier for her to address the sensitive topics that she writes about", he said.
From her writings it was clear "she had gleaned information on the subject of sexuality from her parents, especially her father, from her friend Jacqueline and from books", the foundation said.
Portraits of Anne (right), her sister Margot (center), and mother Edith (left), inside the Anne Frank House.