Today is the 50th anniversary of the night that Marilyn Monroe sang "Happy Birthday" to President John F. Kennedy, Jr. at the old Madison Square Garden, between 50th and 51st Streets. After she performed, JFK took the stage and announced, "Thank you. I can now retire from politics after having had 'Happy Birthday' sung to me in such a sweet, wholesome way." To commemorate the night, LIFE has just published a series of Bill Ray's rare photos from the event. They write:

35-year-old Marilyn Monroe — literally sewn into a sparkling, jaw-droppingly tight dress — stood in a spotlight on a dark stage. She took a breath, began to sing — and 15,000 men and women who filled the old Madison Square Garden that night knew, simply knew, that they were seeing and hearing something that they would never, ever forget.

Jackie Kennedy wasn't in attendance that night, and the evening fueled rumors that JFK and Marilyn were having an affair. Marilyn died three months later, leading to certain conspiracy theories, and JFK was assassinated the next year.