(From CNN.com)

-- South Carolina Gov. Mark Sanford admitted Wednesday, amid speculation over his whereabouts for the last several days, that he has been engaged in an extramarital affair with an Argentinian woman.

Gov. Mark Sanford chokes up as he admits to having an affair.

"I've been unfaithful to my wife," Sanford told a news conference in Columbia, the state capital. "I developed a relationship with what started as a dear, dear friend from Argentina."

His voice choking at times, Sanford apologized to his wife and four sons, his staff and supporters, and said he would resign immediately as head of the Republican Governors Association. The affair was discovered five months ago, Sanford said.

The South Carolina governor had not been seen in public since June 18. When questioned, Sanford's staff had told media outlets that he was hiking in the Appalachian Trail. But Sanford was spotted Wednesday in Atlanta's Hartsfield-Jackson International Airport.

The South Carolina governor said he had been in Buenos Aires, Argentina.

"I'm a bottom-line kind of guy. I'll lay it out, it's going to hurt, and we'll let the chips fall as they may," Sanford said as he spoke with reporters.

The South Carolina governor has had a bruising year, losing his fight to turn down $700 million in federal stimulus money. Sanford initially tried to require that any stimulus money pay down the state debt, a stance rejected by the Obama administration.

The South Carolina's Supreme Court ruled earlier this month that Sanford had to accept the stimulus funds.

Earlier Wednesday, South Carolina Democratic Party Chair Carol Fowler said in a statement it was the "height of irresponsibility for the governor to walk out on his solemn duty to the people of South Carolina.

"When it comes to the real needs and concerns of South Carolinians, Mark Sanford has been pretty much missing in action for the last six-and-a-half years. But it is not acceptable for him to be actually missing.

"However, as disturbing as it is to walk out on your responsibilities without telling anyone, what's more troubling is that the governor and his staff have been less than truthful about his whereabouts," the statement said.

"I am being a mom today. I have not heard from my husband. I am taking care of my children," she said outside the couple's beach home on Sullivan's Island, South Carolina.