It may not be Hollywood's most enduring mystery, but the truth can finally be revealed over why Elvis Presley's trademark quiff turned from near-blond to jet black in the 1956 classic Love Me Tender - he was allowed to do his own hair.

The revelation is one of many Tinseltown secrets in a treasure trove of documents belonging to 20th Century Fox that are to be auctioned in New York next month to benefit an actors' charity.

Alongside details of Elvis's follicular faux pas are letters chronicling Judy Garland's slide into alcoholism, contracts showing the bumper pay packets of Marlon Brando and Cary Grant, and a 1946 memo declaring that Norma Jean Dougherty would henceforth be known as Marilyn Monroe.