Robert F. Kennedy, left, Marilyn Monroe and President John F. Kennedy in 1962 photo taken by Cecil Stoughton. Historian Arthur Schlesinger is on the far right. Singer Harry Belafonte can be seen facing the camera in the rear (Courtesy Keya Morgan via CNN / May 19, 1962)

LOS ANGELES -- A rare photo was unveiled to the public Tuesday, showing Marilyn Monroe with President John F. Kennedy and his brother Robert F. Kennedy at JFK's 45th birthday celebration. It was the same night, May 19, 1962, that Monroe sang her sulty rendition of "Happy Birthday" to the president.

The black-and-white photo, taken by White House photographer Cecil Stoughton, shows Monroe wearing the same sheer rhinestone-studded dress she wore when singing earlier at Madison Square Garden.

The birthday celebration marked the actress' last major public appearance before her mysterious death in August 1962.

The image, which is now up for sale, is the only known photograph of Kennedy and Monroe together, perhaps because of the rumors of an affair that have swirled for 50 years.

"There is no other known photo of Bobby [Kennedy] with Marilyn or JFK with Marilyn, and it's not because they were never photographed together," filmmaker Keya Morgan, who now owns the only original prints of it told CNN. "In fact, they were photographed together many times, but the Secret Service and the FBI confiscated every single photograph."

Stoughton, who sold the prints to Morgan a year before his death in 2008, told him agents missed one negative in their search, he said.

"The Secret Service came in when he was developing the negatives and basically confiscated all the ones of Jack, Bobby with Marilyn," Morgan said. "The only one that survived is the one that was in the dryer," CNN reports.

While the relationship between the Kennedy brothers and Monroe has become a documented part of history, photographer Stoughton was reluctant to allow the image to become public until after former first lady Jacqueline Kennedy's death in 1994.

Morgan told CNN he bought access to the negative while working on an upcoming documentary about the actress' death, "Marilyn Monroe: Murder on Fifth Helena Drive."

Morgan's prints show details not clear in low-resolution, cropped copies that made their way onto the internet after the photo was licensed for a book about Monroe in 2004.

Since Stoughton was a U.S. Army captain and was using a government-owned camera and film, the images themselves are in the public domain. But access to the negative, which Stoughton secretly kept, was valuable.

Stoughton made and signed 10 prints for Morgan, 30 inches by 30 inches. Nine of them go on sale Tuesday at the Art & Artifact Gallery in West Hollywood.

The 10th print was given to singer Michael Jackson two years ago, Morgan said. Morgan was a friend of the pop star's, who was a big Monroe fan.