In Total Recall: My Unbelievably True Life Story, the former Republican governor of California, 65, confirms he had a "hot affair" with costar Nielsen in the 1985 film Red Sonja, the Associated Press reports. At the time, Schwarzenneger was dating and living with his now estranged wife Maria Shriver.
Nielsen, 49, wrote about their "outrageous affair" in her memoir last year, but Schwarzenegger never confirmed.
In his memoir, Schwarzenegger says their "fling" made him realize he wanted to marry Shriver. Nielsen went on to marry Schwarzenegger's friend Sylvester Stallone, but the couple split after 19 months of marriage.