Marilyn Monroe Sex Tape with JFK & RFK: Headed to Auction!

An alleged Marilyn Monroe sex tape is ready to hit the open market, with former President John F. Kennedy AND his brother Robert F. Kennedy in co-starring roles.

It's not entirely clear if JFK and RFK tag-teamed Marilyn Monroe at the same time, or if the same video just happens to contain separate trysts with the brothers.

Either way, former Hollywood bodyguard William Castleberry says it's legit, and was just seized from his home along with other property as a result of a lawsuit.

The Marilyn Monroe sex tape is going to auction Tuesday to cover a $200,000 court judgment against him, unless he can come up with that sum beforehand.

No offense William ... but we're not exactly pulling for you here.

Castleberry won't say where or how he got the film, but says he always kept it secret out of respect for her ex-husband Joe DiMaggio, who he says was a good friend.

The steamy footage has never before been seen ... obviously.

William says he's well aware that a lot of people will think he's a fraud, but insists it's definitely the sexual icon, who died in 1962 at age 36, on the 8mm film.

There have long been rumors that the Hollywood legend had affairs with both Kennedy brothers in the early '60s, so this wouldn't be totally unrealistic, but ...

Let's just say the Kim Kardashian sex tape remains the gold standard until we see actual proof of JFK, RFK or MM going to town on each other on film.