The four-page letter to longtime Kennedy family friend Mary Pinchot Meyer, an artist and former wife of a CIA agent, is thought to have been written in October 1963, about a month before the president's assassination.
"Why don't you leave suburbia for once come and see me either here or at the Cape next week or in Boston the 19th," the letter reads.
"I know it is unwise, irrational, and that you may hate it on the other hand you may not and I will love it. You say that it is good for me not to get what I want. After all of these years you should give me a more loving answer than that. Why don't you just say yes."
"It's incredible to see the president writing something so personal," said Robert Livingston, the executive vice president of Boston-based RR Auction , which is handling the sale. "We've handled a lot of JFK letters here, and he was always very formal."
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The undated letter looks to be written on White House stationery. Although the tops of each page have been cut off, the presidential seal watermarks are visible under light.
The letter was never sent but remained in the collection of Kennedy's longtime personal secretary, Evelyn Lincoln. It originated from the estate of Robert White, a friend of Lincoln's and an avid collector of JFK memorabilia who died more than a decade ago.
The letter is expected to fetch about USD 30,000 in the weeklong online auction that starts June 16, Livingston said.