Cheryl Hines is ready to walk down the aisle with her famous fiancée, Robert F. Kennedy, in a Cape Cod, Mass., wedding this summer— but the Hollywood actress may want to change her plans.

According to The National ENQUIRER, Kennedy, 60, has been cheating on Hines, 48, with a 42-year-old divorcee he met at his Armonk, New York gym!

“He turned on the Kennedy charm to woo her into the sack. He’s a no-good horn dog!” a source tells The ENQUIRER, adding that the attorney carried on the affair with the sexy mother of four for nearly two years.

Though Kennedy and Hines carried on a high-profile romance, the insider says the mistress had no idea her man was in a serious relationship.

“She’s been terribly hurt by being led on by Bobby,” the source explains. “She really liked him, and now realizes he’s a cad for giving her false hope that they might have a future together. He’d even hinted that marriage was a possibility.

Kennedy and Hines began dating in 2012, months before Breaking Celebrity News exclusively reported that his estranged wife, Mary Richardson, tragically committed suicide in their Mount Kisco, New York home at just 52.