In a stunning world exclusive, The ENQUIRER reveals that Robert F. Kennedy Jr. has been embroiled in a sordid cheating scandal on the eve of his high-profile wedding to TV beauty Cheryl Hines!

The Kennedy scion has a history of womanizing, and a source says he’s at in again.

“It boggles the mind that just weeks before his wedding to Cheryl, Bobby is willing to risk everything,” noted the source, who filled us in on details of the alleged affair.

Kennedy, a 60-year-old environmental lawyer/activist, began his relationship with “Curb Your Enthusiasm” star Cheryl, 48, while he was estranged from his tragic second wife Mary, who hanged herself in 2012.

The son of the late politico Robert F. Kennedy reportedly enjoyed numerous affairs while wed to Mary – and he allegedly compiled a sex diary in which sources say he admits to being a serial cheater who’s controlled by “lust demons.”

Despite his checkered past, Robert and his glamorous fiancée are planning to exchange vows this summer during the annual Kennedy clan reunion in Hyannis Port, Mass.

As always, The ENQUIRER goes behind the scenes to provide you with inside information you won’t find anywhere else. So be sure to pick up a copy of our latest issue today!