July 29, 2009  -- What began as a government internship for a one-time honors student with a questionable past has become a full-blown sex scandal that ensnared a married Tennessee state senator and led him to resign.

Republican Sen. Paul Stanley had maintained a low profile until his announcement late Tuesday that he was resigning from the state Senate effective Aug. 10, after his affair with a 22-year-old intern and a subsequent extortion attempt was revealed to the public.

Stanley, a 47-year-old evangelical Christian with two children, said in his resignation letter that he has "decided to focus my full attention on my family."

"Whatever I stood for and advocated, I still believe to be true," he told Memphis radio station WREC-AM Tuesday. "And just because I fell far short of what God's standard was for me and my wife, doesn't mean that that standard is reduced in the least bit."

He had been engaged in a sexual relationship with intern McKensie Morrison when her boyfriend, Joel Watts, contacted him, according to an affidavit filed in Davidson County by prosecutor Douglas Long.

Watts threatened April 8 to release nude photos of Morrison at the senator's apartment unless Stanley paid him $10,000, the affidavit claimed.

Watts, 27, allegedly discovered a memory disc with explicit photos of Morrison that were taken in Stanley's apartment on a cell phone. "Watts communicated to Stanley if he did not pay the money, the photographs would be sent to other individuals, including the media," the document states.

"Good morning, sir. How are you this fine day? McKensie and I have been talking, and I feel that I have a video and some pictures you might be interested in seeing," Watts allegedly texted to Stanley, according to a transcript read aloud during the hearing, as reported by The Associated Press.

Tennessee Senator's Sex Scandal

Instead, Stanley contacted the Tennessee Bureau of Investigation.

"He came to us for help," TBI spokeswoman Kristin Helm told ABCNews.com. "We explained to him that we were going to take that information to the district attorney general who did turn around and ask us to open an investigation."

After recovering the threatening text messages, TBI instructed Stanley to play along with Watts' demands, according to court documents.

The TBI provided Stanley with the $10,000 Watts had requested and on April 9, the two met behind a Mexican restaurant to exchange the money for the disc. Once the cash and the disc were swapped, Watts was arrested, charged with theft of property and extortion.

After a preliminary hearing last week, Watts' case was sent to a grand jury for extortion. The theft charge was dismissed.

Neither Watts nor Morrison could be reached for comment.

ABC News' Nashville affiliate WKRN reported that Stanley released a statement last week, saying he was "the victim and a witness to a crime."

"At this time, I have been advised by authorities and the district attorney's office not to comment. There is already misinformation being inferred regarding this matter which I look forward to clearing up at the appropriate time," the statement read.

Lt. Gov. Ron Ramsey's office also declined to return repeated messages today.

But Ramsey, who is also the speaker of the Senate, told Tennessee media at a fundraiser this past weekend that he considered Stanley to be a close friend and that Stanley had been having marital problems for some time.

"First of June, end of May he was in my office, he told me he and his wife were going to be separated," said Ramsey, "and obviously we had a good conversation about that. Both of us were upset about that."

Helm said Stanley was "very cooperative" throughout the investigation, adding that the TBI's active investigation is now closed and she does not expect Morrison to be charged at this time for playing a role in the senator's alleged extortion.

Cop Says No Evidence to Charge State Senator's Mistress

"I don't really know what her involvement was as far as how much she played a part," Helm said. "But obviously, if we had the evidence to charge her at the time Joel Watts was charged, we would have charged her."

Morrison is no stranger to controversy. According to an article published this week in the Orlando Sentinel, the former central Florida high school honors student has been arrested for cocaine possession and was married to a man who is now in prison for beating a 75-year-old man in the head with a hammer in her presence.

Though Stanley is a state-level politician, he joins the ranks of numerous other elected officials who have made more headlines for their dalliances with mistresses than for their policy-making.

South Carolina Gov. Mark Sanford came under fire not only for admitting to an affair with an Argentinean mistress, but for disappearing with her on vacation without telling staffers and then apologizing in a drawn-out, nationally televised press conference.

Last year, former presidential candidate John Edwards finally owned up to an affair with campaign staffer Rielle Hunter after more than two years of denying that he was cheating on his terminally ill wife, Elizabeth Edwards.