Arnold Schwarzenegger's mistress broke down and admitted, during a showdown with his wife, Maria Shriver, that she had his love child, US media reports
The couple's housekeeper, Mildred Patricia Baena, known as Patty, confessed when Ms Shriver asked her whether her son was fathered by Mr Schwarzenegger.
Ms Shriver then confronted her husband, who also admitted it, Radar Online reported.
"Maria has suspected this for a long time and she asked the housekeeper," the website quoted a source as saying.
"The housekeeper admitted it.
"Maria then went to Arnold and he confessed.
"He didn't volunteer the information, and it could have remained a secret if Maria hadn't asked."
Despite its earlier reports, the gossip website said that Mr Schwarzenegger did not fire the housekeeper in order to save his marriage, but that her employment ended "without acrimony".
The former California governor and Terminator star bought Ms Baena a $US300,000, four-bedroom house in Bakersfield as a retirement gift, The Sun reported.
The 50-year-old housekeeper and the 13-year-old boy moved in there while she was still working for Mr Schwarzenegger and Ms Shriver and she retired six months later.
Ms Baena worked in Mr Schwarzenegger's Brentwood mansion for 20 years doing cooking, cleaning and laundry, reportedly earning more than $1100 a week.
Her home - about 200 kilometres from her former workplace - has a pool and two garages, neighbours said.
Resident Marty Steelman, whose husband designed the house, said she could now see the resemblance between the boy and his father.
"It's amazing to think Arnold Schwarzenegger's son has been living in the house next door to us all this time."
CNN said it obtained documents that show Ms Baena gave birth less than a week after Ms Shriver had her youngest son.
The birth certificate for Ms Baena's son said the boy's father was the man she was married to at the time, but divorce papers said the pair split about three weeks after the boy was born on October 2, 1997.
Ms Shriver, who this week appeared onstage with Oprah Winfrey for the TV queen's final show, has reportedly hired prominent divorce lawyer Laura Wasser, who has handled the divorces of Britney Spears and Angelina Jolie.
The Telegraph reported Ms Shriver was struggling with the idea of getting a divorce because she is a Catholic and had not yet decided whether to end her marriage.
Meanwhile, Mr Schwarzenegger has decided to put his acting career on hold.
"At the request of Arnold Schwarzenegger we asked Creative Artists Agency to inform all his motion picture projects currently under way or being negotiated to stop planning until further notice," his entertainment lawyer, Patrick Knapp, told US media in a statement.
Follow Life&Style on Twitter @Life_Style_News