The items will be available for purchase on the internet along with hundreds of other historical documents, reported Aceshowbiz.
In her letter, Monroe said she was losing the will to live, "My will is weak but I can't stand anything. I sound crazy but I think I'm going crazy. It's just that I get before a camera and my concentration and everything I'm trying to learn leaves me. Then I feel like I'm not existing in the human race at all."
As for Lennon's letter, it reflects the deep tension between the late musician and bandmate McCartney.
"Do you really think most of today's art came about because of The Beatles? I don't believe you're that insane - Paul - do you believe that? When you stop believing it you might wake up!" he wrote.
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The note was actually a two-page draft letter that was typed on a letterhead stationary with a picture of Lennon and his wife Yoko Ono. The undated and unsigned note is expected to sell around USD 40,000 to USD 60,000.
Other items are Dwight D Eisenhower's handwritten letters during World War II about news of the war and his devotion to his wife Mamie, and two big photo albums exchanged by Adolf Hitler and Benito Mussolini before the war erupted.