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The salacious secrets are out.
Hugh Hefner's little black book is now on display as of the Chicago History Museum's "Unexpected Chicago" series.
Hefner, perhaps the most famous bachelor of all time, founded Playboy in Chicago in 1953, and the black book was compiled as his magazine began to thrive and celebrity was on the rise.
The book includes real names and pseudonyms, notes to himself to help identify women he met, basic contact information and code words presumably meant to identify a tryst, according to Crain's.
The book was obtained from Christie's in 2003 and is the latest addition to the Museum's collection of 22 million artifacts in the exhibit.