The first, with housekeeper Mildred Baena, resulted in a child who's now a teenager, it was revealed last year. The second fling, according to the book, was "a hot affair" with actress Brigitte Nielsen when she and Schwarzenegger co-starred in the 1985 film Red Sonja. Nielsen first divulged their dalliance in her own memoir, which was released last year. Schwarzenegger and Shriver were dating and living together at the time, according to the Associated Press, but were not yet married.
In an interview with 60 Minutes to promote the book, Schwarzenegger calls his infidelity with Baena "the stupidest thing I've done in the whole relationship."
"It was terrible," the former governor of California admits. "I inflicted tremendous pain on Maria and unbelievable pain on the kids."
Shriver filed for divorce in May 2011 after learning that Schwarzenegger had fathered a child with Baena. The couple were married for 25 years.
Schwarzenegger's full 60 Minutes interview airs Sunday at 7/6c on CBS. Watch a clip below: