Maria Shriver was reportedly sleeping with Arnold Schwarzenegger's lead campaign strategist long before his affair with the couple's housekeeper came out.
Shriver, 58, publicly debuted her new boyfriend, Matthew Dowd, last month at her cousin Bobby Kennedy Jr's wedding amid reports the pair had been seeing each other for less than a year.
But according to the New York Post, the Kennedy heiress started her relationship with Dowd back in 2006 while he was working as chief strategist for Schwarzenegger's gubernatorial re-election campaign.
"Maria likes to make it appear that she's the victim, but she's not," an unnamed source told The Post.
"The (idea) that they started dating recently is ridiculous."
Shriver, the niece of Robert F Kennedy and President John F Kennedy, continued the rendezvous even after Schwarzenegger found out, the newspaper claims.
After the 67-year-old Terminator star won a second term as governor of California, he and his wife allegedly remained together in public, while she continued to see the twice-divorced Dowd on the side.
Shriver and Schwarzenegger split in 2011 after the actor admitted to bedding the family's maid, Mildred Beana, years earlier and fathering her son, who is now 16.
The divorce hasn't been finalised but the pair, who have three children together, have been living apart since the actor went public with his love child.
Dowd, who was one of the masterminds behind George W Bush's 2000 and 2004 presidential campaigns and now works as a political analyst for ABC News, has denied the affair and told The Post they were no more than "good friends" in 2006.
Neither Shriver nor Schwarzenegger have commented.