A sex video of Marilyn Monroe hit the auction block — and it's a doozy. It features not only the legendary screen siren, but also a married John F. Kennedy and his brother, Robert Kennedy ... both reportedly engaging in a sexual intercourse threesome with the fallen star.

Memorabilia collector William Castleberry claimed he owns the only copy of an 8 mm. sex video of Monroe, RFK and JFK, and that it nearly hit the market when he was in debt, because it was part of his possessions seized and sent to auction.

The sex tape was slated to hit the auction block today (Tuesday, March 4).

Castleberry explained that he faced a $200,000 judgement for allegedly selling a fake statue to several people in Visalia, Calif. Castleberry says he'd made payments on his debt, but that lawyers demanded a balloon payment that was worth more than most people make in a year.

The collector in collections griped, "They demanded a $90,000 payment I couldn't afford, and that is when the sheriff came in and seized the sex tape and all of my other memorabilia I have been collecting my entire life."

Castleberry kept this particular sex video secret forever because he claims to have been friends with Monroe's former husband, Joe DiMaggio.

Of course, no one has seen the video yet to verify whether or not it's legit, but Castleberry told Radar Online, "It's real. I had it for years and I never released it out of respect for Joe DiMaggio… I'm just sick about it and I'm desperately trying to raise money to get it back."

It's not the first time Monroe has been the rumored subject of a sex video. An alleged pornographic video of the icon was attempted to be auctioned in 2011, but was deemed to be fake and had no takers. Monroe was also rumored to star in a black and white film giving oral sex to someone mostly off-camera who was said to be a Kennedy brother, but its existence was never confirmed and it hasn't seen the light of day ... and the owner refused to release it. Maybe it was Castleberry!

Castleberry would be wise to never, ever convert that alleged film to digital ... or else Farrah Abraham and Kim Kardashian will have runs for their sex selling money.

More from YourTango: