Alleged Marilyn Monroe sex tape with John Kennedy, Robert Kennedy up for auction Tuesday

Marilyn Monroe, John F. Kennedy and Robert F. Kennedy's alleged three-way sex tape is up for grabs.

According to a report in The Telegraph, Spanish collector Mikel Barsa is looking to sell the six-and-a-half-minute, black-and-white 8mm film for $500,000 (£306,500).

The sex tape will be auctioned off Tuesday along with other memorabilia saved by Barsa (identified as William Castleberry by TMZ.com and The Daily Mail).

Barsa, who earlier served as a bodyguard in Hollywood, claims that the film was made before 1947, when the enduring actress had yet to turn 21.

Experts are currently split on whether or not the woman is in fact Monroe, with one noting that the woman featured in the video is heavier than the star was.

Basra defends it, however, saying the film predates Monroe's transformation into the icon remembered today.

"The Marilyn that everyone recognizes is not the Marilyn seen [in this film], because she underwent a great transformation," Barsa told the publication.

Scott Fortner, who has a considerable collection of Monroe collectibles, told The Telegraph: "If you look at the chin line, at the jaw line, at the teeth of the woman in the film and compare that to Marilyn you can clearly make some distinctions."

Although Barsa refused to disclose the owner of the tape, the Sheriff's Office in Tulane County reportedly seized it along with other items from the collector's home when he defaulted on a debt.

Incidentally, this video is not the only existing pornographic film attributed to Monroe, who died at the age of 36 in 1962. Another 15-minute sex tape supposedly shot in the 1950s was sold for $1.5 million in 2008.