Missouri Gov. Eric Greitens, a sometimes brash political outsider whose unconventional resume as a Rhodes scholar and Navy SEAL officer made him a rising star in Republican politics, abruptly resigned Tuesday amid a widening investigation that arose from an affair with his former hairdresser.

The 44-year-old governor made the announcement nearly 17 months after taking the oath of the office with a pledge to root out "corrupt career politicians." The probes into his conduct by prosecutors and lawmakers began with allegations stemming from the affair. They soon expanded to include questions about whether he had violated campaign-finance laws.

Greitens said his resignation would take effect Friday.

"This ordeal has been designed to cause an incredible amount of strain on my family — millions of dollars of mounting legal bills, endless personal attacks designed to cause maximum damage to family and friends," he said in a brief statement from his Jefferson City office, his voice breaking at times.

Lawmakers pressuring Greitens to step down included many Republicans, who feared that his troubles could jeopardize the party's chances of defeating incumbent Democrat Sen. Claire McCaskill in a state won handily by President Donald Trump.

A St. Louis grand jury indicted Greitens on Feb. 22 on one felony count of invasion of privacy for allegedly taking a photo of the woman without her consent at his home in 2015, before he was elected governor. The charge was dismissed during jury selection, but a special prosecutor was considering whether to refile charges.

In April, the local St. Louis prosecutor's office charged Greitens with another felony, alleging that he improperly used the donor list for a charity that he had founded to raise money for his 2016 campaign.

Then less than two weeks ago, the Missouri Legislature began meeting in special session to consider whether to pursue impeachment proceedings to try to oust Greitens from office.

A special House investigatory committee had subpoenaed Greitens to testify next Monday.

Republican leaders in the Missouri House said Greitens had "put the best interest" of the state first in deciding to resign. His brashness had alienated some GOP legislators even before his affair became public in January.

The woman's then-husband released a secretly recorded conversation in which she described the affair. The woman later told a Missouri House investigative committee that Greitens restrained, slapped, shoved and threatened her during a series of sexual encounters that at times left her crying and afraid.

Greitens said the allegations amounted to a "political witch hunt" and vowed to stay in office. But a report from a House committee created a firestorm, with both Republicans and Democrats calling for his resignation.

His departure elevates fellow Republican Lt. Gov. Mike Parson to the governor's office.

Greitens' administration was thrown into chaos the night of Jan. 10, when a St. Louis TV station aired a report about Greitens allegedly taking the compromising photo and threatening to blackmail the woman if she ever spoke of their encounter. The report aired shortly after Greitens delivered his State of the State address.

The governor admitted to having an affair but denied any criminal wrongdoing. He said the criminal case was politically motivated and called St. Louis Circuit Attorney Kim Gardner, a Democrat, a "reckless liberal prosecutor."

Lawmakers from both parties immediately began questioning whether Greitens could continue to lead the state. The House authorized the legislative investigation a week after the indictment.

Missouri Attorney General Josh Hawley also launched an inquiry into a veterans' charity Greitens founded. Federal law bars 501(c)(3) charities such as The Mission Continues from intervening in political campaigns on behalf of candidates.

The Associated Press first reported in October 2016 that Greitens' campaign had obtained a list of individuals, corporations and other nonprofits that had given at least $1,000 to The Mission Continues. The AP reported that Greitens raised about $2 million from those who had previously given significant amounts to the charity.

Hawley, a Republican running for U.S. Senate, turned evidence over to Gardner, saying April 17 that he believed Greitens had broken the law. Her office charged him with tampering with computer data for allegedly disclosing the donor list without the charity's permission.

A May 2 report from a special House investigatory committee indicated that Greitens himself received the donor list and later directed aides to work off it to raise money for his gubernatorial campaign. A former campaign aide testified that he was duped into taking the fall when the campaign tried to explain how it had gotten the list.

The invasion-of-privacy indictment alleged that on March 21, 2015, Greitens photographed the woman and transmitted the photo "in a manner that allowed access to that image via a computer."

During her testimony to the House investigative committee, the woman said Greitens invited her to his home and offered to show her "how to do a proper pull-up." The woman said she initially thought "this is going to be some sort of sexy workout."

But once in his basement, Greitens taped her hands to pull-up rings, blindfolded her, and started kissing and disrobing her without her consent, according to her testimony.

Then she saw a flash and heard a click, like a cellphone camera, she said. The woman testified that Greitens told her: "Don't even mention my name to anybody at all, because if you do, I'm going to take these pictures, and I'm going to put them everywhere I can. They are going to be everywhere, and then everyone will know what a little whore you are."

Greitens, a married father of two young boys, repeatedly denied blackmailing the woman. He declined to say whether he took a photo.

The governor, who also served as a White House fellow and wrote a best-selling book, entered the 2016 gubernatorial race as an outsider. He won an expensive Republican primary, then defeated Democratic Attorney General Chris Koster in the general election to give Republicans control of the governor's mansion for the first time in eight years. Some considered him a potential future presidential contender.

Republicans also controlled the Missouri House and Senate, but there were frequent clashes between lawmakers and Greitens, who compared them to third-graders and labeled them "career politicians."

He confronted criticism from some educators and lawmakers for working to pack the State Board of Education with members who would fire the education commissioner. Greitens' use of a secretive app that deletes messages after they're read also sparked a review by Hawley.