(abc) Apologizing profusely to his staff, family and friends for disappearing unexpectedly, a teary-eyed South Carolina Gov. Mark Sanford said he had been "unfaithful" and admitted affair with a woman in Argentina. "I've been unfaithful to my wife," Sanford said at a press conference this afternoon, adding that his affair was with a "dear, dear friend from Argentina." The affair, Sanford said, began "casually" but "last year developed into something much more." "We developed a remarkable friendship over those eight years and then as I said about a year ago it sparked into something more than that," Sanford explained. "I have seen her three times since then, during that whole sparking thing. ... It was discovered five months ago and went into serious overdrive." Sanford also offered his resignation from his position as chairman of the Republican Governors Association.