WASHINGTON — The FBI sent memos warning then-attorney general Robert Kennedy about an upcoming book about the death of Marilyn Monroe and his alleged “intimate relationship’’ with the movie star, according to recently released files.

Kennedy, the younger brother of President John F. Kennedy, was informed about the book in July 1964, memos show. According to the memos, the book, “The Strange Death of Marilyn Monroe,’’ by Frank A. Capell was set to be released in July 1964.

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Robert Kennedy was told the 70-page book included allegations that he had an affair with Monroe and that he was in her apartment when she died, the memos show.

The memos, however, said Kennedy was in San Francisco with his wife when Monroe died.

The memos said Capell claims in the book the Kennedy-Monroe affair “was well known to her friends and reporters in the Hollywood area,’’ but was never publicized.

Monroe died on Aug. 5, 1962 of an overdose of barbiturates. Police ruled it a probable suicide. The circumstances of Monroe's death have been controversial and plagued by conspiracy theories.

Robert Kennedy was also provided background information about Capell, according to the memos.They also indicate that Capell had been interviewed by several agents about allegations he also made about other high-profile people.

“Much of the information furnished by Mr. Capell has been of a very questionable nature and not subject to corroboration,’’ according to the memo. “He has consistently refused to reveal the alleged sources of his information. The FBI said it would “promptly’’ inform Kennedy about any more information related to the book.

Contributing: Adam Woodard, Matthew Coyne, Andrew Yawn, Robin Buchanan, Stacey Barchenger, Jason Noble, Algernon D’Ammassa, Matthew Miller, Mary Helen Moore, Mike Ellis, Bianca Medious, Robert King, Kayla Daugherty, Tovah Olson, Kevin Crowe, Bill Theobald, Cayce Berryman, Susanne Cervenka, Lucas Daprile, Doug Schneider, Dana Williams, Emily Bohatch, John Moses, Richard Wolf, David Jackson, Jessica Estepa, Ray Locker, Julia Fair, and Helen Parshall from the Capital News Service.