The notoriously bitchy comedian - who died in 2014 at the age of 81 after suffering a heart attack during a routine medical procedure - rarely apologised for her acid tongue.
But fans will see a softer side to her in new book 'Joan Rivers Confidential', according to The New York Post newspaper.
The autobiography - written by Joan's daughter Melissa Rivers and friend-and-publicist Scott Currie - will feature private letters belonging to the 'Fashion Police' star, sent by the likes of Meryl Streep.
One of the notes to be made public in the book was written by Joan to 'American Horror Story' star Kathy, after she was upset by the comic's joke that the movie version of the 'Titanic' wouldn't have sunk if Kathy had not been onboard.
Joan wrote to Kathy: ''The fact that people even know our names is a gift from God so relax, enjoy your fame and SMILE.
''Please know that I am a loyal, devoted, longtime fan of yours. (P.S. I also took your side in 'Misery.') Love and Kisses, Joan XOXO. (sic)''
Meryl Streep and other celebrities including Tom Hanks, David Letterman and Bo Derek have also given permission for their private letters to Joan to be published.
Meryl wrote: ''Stephen Hawking and I could do a show about black holes, and then, I could disappear into one, a star collapsing in upon itself until it becomes at once invisible and incomparably dense.''
Joan's most catty comments will be celebrated in the book, including her joke about Jennifer Aniston: ''Even if she does become pregnant, Angelina [Jolie] will get the baby.''
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