In his upcoming Netflix docuseries Arnold, the Terminator star shares the moment he admitted to his then-wife that he had an affair and fathered a son, Joseph, now 25, with the family's housekeeper, Mildred Baena.
"Maria and I went to counseling once a week," Schwarzenegger, 75, recounts in the three-part series, per People, "and in one of the sessions the counselor said, 'I think today Maria wants to be very specific about something. She wants to know if you are the father of Joseph.' And I was like—I thought my heart stopped, and then I told the truth."
In fact, the Total Recall star, who wed Shriver in 1986, remembers his direct response: "'Yes, Maria, Joseph is my son.'"
However, he notes that he didn't initially realize he had another son.
"She was crushed because of that," Schwarzenegger continues. "I had an affair in '96. In the beginning I really didn't know. I just started feeling the older he got the more it became clear to me and then it was really just a matter of how do you keep this quiet? How do you keep this a secret?"
Though the former politician is detailing his story now, Schwarzenegger—who also shares kids Katherine, 33, Christina, 31, Patrick, 29, and Christopher, 25, with Shriver, 67—is hesitant about doing so "because every time I do, it opens up the wounds again."
"I think that I have caused enough pain for my family because of my f--k up," he adds. "Everyone had to suffer. Maria had to suffer. The kids had to suffer. Joseph. His mother. Everyone."
As he puts it, "I am going to have to live with it the rest of my life. People will remember my successes and they will also remember my failures. This is a major failure. I had failures in the past in my career, but this is a whole different ball game, dimension of failure."
But Schwarzenegger also makes it clear he has the most praise for Joseph, sharing that he has grown into a "fantastic man."
"It was wrong what I did," the Running Man star explains. "But I don't want to make Joseph feel that he is not welcomed in this world—because he is very much welcomed in this world. I love him and he has turned out to be an extraordinary young man."
The former bodybuilder—who split from Shriver in 2011 and finalized their divorce ten years later—also says in the series he is "very happy" about the way the former couple "were able to raise the kids really well" in the midst of turmoil.
"There is nothing more important than to have a good partner by your side, and every step of the way Maria was that," he adds in the docuseries. "We have a really great relationship."
As for Joseph—who has decided to follow in his dad's footsteps and pursue acting—he recently weighed in on whether the father-son duo would ever unite onscreen.
"Not yet," the Dancing with the Stars alum told E! News exclusively in May, "That's gonna be the next big step."
Arnold, the three-part docuseries, will hit Netflix on June 7.