Marilyn Monroe famously sang a sultry “Happy Birthday, Mr. President” to John Kennedy 48 years ago today. In honor of the anniversary, LIFE magazine has uploaded a slideshow of pictures taken that night by photographer Bill Ray. Most have never been released before.

There are some great shots in the group, and Mr. Ray comments on each picture, providing great detail on the party, the old Madison Square Garden (aka Madison Square Garden III, closed in 1967 and bulldozed in 1989), and the difficulties the press had in getting close to the event.

He had wanted to get a shot of Kennedy watching Marilyn, his reputed mistress, performing but the Secret Service wouldn’t let photographers stay in front of the stage, so he had to wander all over the Garden looking for the one spot that would give him that shot. Finally he found a nosebleed seat behind the stage that had the proper sight lines.

“It had been a noisy place, everybody all ‘rah rah rah,'” Ray recalls. “Then boom, on comes this light. There was no sound — no sound. It was like space.” Marilyn was on the stage, taking off her white fur to reveal that scandalous dress underneath. “It was skin-colored and it was really tight. She didn’t wear anything underneath it, it was all sewn on, and those Swarovski crystals were sparkling. And she used this long pause… Then finally, she comes out with ‘Happy Biiiiirthday’ — she starts the whole breathy thing — and everybody just went into a swoon.” Ray took his shots, including this one and the iconic frame that opens this gallery. “I was praying because I had to guess at the exposure. It was a very long lens, which I had no tripod for, so I had to rest it on a pipe railing and try not to breathe.” Though he couldn’t get the Marilyn/JFK shot he’d initially wanted — “she was in such a bright spotlight and he was almost in total darkness” — Ray still came away with a winner of a picture: “I got very lucky with this,” he says.

Not iconic but awesome nonetheless is his backstage picture of the divine Ella Fitzgerald.

The Marilyn moment tends to eclipse everything that happened before it. But there were many stars on the bill. At some point Ray made his way backstage, where he captured a contemplative Ella Fitzgerald waiting to go on — and looking much more elegant than her surroundings, Ray says. “All of the Garden was old, and the dressing rooms back then were really tacky.”

They almost look like mirror images or bizarro opposites, don’t they? The way they’re holding their arms; one shot from behind, one from the front; one onstage, one backstage; Marilyn in white(ish), Ella in black.