She is an intensely private woman who was not afraid to fight back when that privacy was breached.
She was educated in Catholic schools and professes her belief in God, evil and the afterlife, and yet joined a married father of four in violating the Seventh Commandment prohibition against adultery.
Maria Belen Chapur has successfully eluded the news media since South Carolina Gov. Mark Sanford revealed their yearlong affair last week. Friends and family have enfolded her and her boys in a protective cocoon, and the only image of her is a grainy, 8-year-old video from her brief moment in front of the cameras as a television reporter in New York.
Other than a 200-word statement denouncing a hacker's "evil act" of leaking her passionate e-mail correspondence with Sanford, Chapur has maintained her silence.
"I won't speak about my private life as it just belongs to me," she wrote to a former television colleague. "It has already been made too public during these last days, bringing to me even more pain."
Due partly to the loyalty of friends and family, and Argentine privacy laws, relatively little is known about Sanford's "other woman." In fact, much of what we know about Chapur comes from her purloined personal e-mails.
As a child, Chapur attended St. Catherine's Moorlands, a private, international baccalaureate school in Buenos Aires. Chapur's mother is from what one acquaintance described as a very powerful "oligarchic" family in Argentina.
After school, she married a grain exporter and bore two sons, now 15 and 19. Later, Chapur entered the Catholic University of Argentina, says a former classmate, graduating with a degree in political science and international relations.
The athletic, dark-haired Chapur traveled the world, learning English, French and Portugese. She even studied Mandarin Chinese after accompanying her husband on a business trip to Beijing and Shanghai.
"It was like playing mimics all the time," she told The Associated Press in a 2005 story about Argentines rushing to study Chinese. "I've traveled to many parts of the world, but this was the hardest place for me to communicate."
Chapur dabbled in television, reporting from New York in the aftermath of the 9/11 terrorist attacks, and also did stints as an English interpreter and market researcher.
She and Sanford met eight years ago, according to one of Sanford's e-mails, "in a wind swept somewhat open air dance spot" in Punta del Este; an upscale Uruguayan beach resort that attracts up to 1 million visitors in the South American summer.
Sanford had just finished his third term in Congress and was about to embark on his first gubernatorial campaign. Chapur was separating from her husband, and Sanford counseled her that she should try to salvage her marriage for the boys' sake and because it was "part of God's law."
For whatever reason, that reconciliation never happened, and the couple divorced. But her e-mail correspondence with Sanford continued, and intensified.
In June 2008, a relationship that started out innocently and in Sanford's words, "developed into something much more than that."
That month, Sanford traveled to Brazil on a state trade mission. He managed to build in a side trip to Buenos Aires.
The governor's agenda includes hours of "personal time" and two dinners where he advises others to have "dinner on your own." Receipts show he listed no other state officials joining him at El Faro restaurant and el Mosto wine bar; both in the Hilton Buenos Aires, where he stayed for three nights that weekend.
Despite her accomplishments, this well-mannered polyglot and competitive runner was confused and full of self-doubt.
"You are glorious and I hope you really understand that," Sanford wrote her a few days later in one of the e-mails, which were sent anonymously to The State newspaper in the South Carolina capital. "You do not need a therapist to help you figure your place in the world. You are special and unique and fabulous in a whole host of ways that are worth a much longer conversation."
Responding to "My beloved" later that day from Ilhabela, an exclusive island resort in Brazil, Chapur sounded like a giddy schoolgirl.
"As I told you before, you brought happiness and love to my life and (I) will take you forever in my heart," she wrote in conversational, but imperfect English. "Believe me, I haven't felt this since I was in my teen ages, when afterwards I got married."
She sent Sanford her mailing address, promising that if he sent her something, to "keep it near my bed so as to feel you nearer." She closed professing love "from the deepest of my heart" and "Sweet kisses."
Five days later, Chapur confided that she was at the island with another man, but told Sanford "you are my love ... something hard to believe even for myself as it's also a kind of impossible love, not only because of distance but situation."
And when Sanford apologized for "complicating" her life, she said "on the contrary you've fullfiled me with happiness and made me aware how you can feel when you love somebody."
Thanking Sanford for making their "hopelessly impossible" become a reality, she said "I prefer to think we'll see each other again somewhere sometime in this life and in next."
Since word of the affair broke last Wednesday, first lady Jenny Sanford has been widely praised for her poise and strength. She has fiercely guarded her sons' privacy, and expressed a willingness to work at forgiving Sanford and salvaging the marriage.
Chapur, who bears an uncanny resemblance to Mrs. Sanford, has demonstrated similar fortitude and grace, despite her role in this drama.
While a horde of reporters laid siege to her trendy apartment building across from Buenos Aires Zoo in the upscale Palermo Botanico district, Chapur low in another family home. And in a country where it is not uncommon for media to pay big for such a story, she kept her mouth shut as reporters speculated, often wrongly, about the mistress's identity and who leaked the e-mails.
Finally, on Sunday, she had had enough.
"I have decided to send to you this release that will be the only one," she wrote to C5N executive Eduardo Feinmann, "to thus clarify certain incorrect things that are being spread worldwide so as to give an end to the subject that as you can imagine is of great pain to me, as for my two children, my family and all the great friends that I have known and harvested throughout my life and that had always been there for me."
Contrary to reports that their e-mail had been leaked by the other man she mentioned to Sanford, Chapur revealed that someone else had "hacked" into her and seized control of her old Hotmail account in late November. She believes that same person then sent the stolen e-mails in December to the South Carolina newspaper and the other lover.
"Far away from being the author of this evil action," she said, "he was instead another victim."
Chapur filed a series of formal complaints against an Argentine Internet service provider and worked through Microsoft to regain control of the e-mails and close down the account.
Despite having strong suspicions about who "may have done this great damage" to her and others, Chapur said she doesn't have enough proof to expose the hacker.
"I am not the one to judge anyone," she concluded. "I leave this in God's hands."
Many who have watched his tearful, dejected public confessionals believe Sanford is still in love with Chapur.
If she feels the same, she is not saying.