Alabama's governor, embroiled in impeachment proceedings that began Monday, resigned Monday afternoon amid a criminal probe into claims of misuse of state resources to pursue and later cover up his affair with a former staffer.

Allegations of the affair with Rebekah Caldwell Mason, which consumed his administration for more than a year, broke up GOP Gov. Robert Bentley's marriage of 50 years in 2015. Lt. Gov. Kay Ivey will become Alabama's second female governor and its first female Republican governor when she is sworn in at 6 p.m. CT.

On Monday afternoon, Bentley was booked into Montgomery County Jail on two misdemeanor campaign finance charges. He pleaded guilty to failing to file a major campaign finance report and converting campaign money for personal use, was sentenced to a 30-day suspended sentence and 12 months of unsupervised probation, ordered to pay $50,000 in fines and must serve 100 hours of community service.

The misdemeanor sentence means that Bentley, a dermatologist since he left the U.S. Air Force, will be able to keep his medical license.

Bentley's governorship became increasingly overshadowed by allegations he pursued an affair with Mason, attempted to use state resources to aid it, and tried to persuade state law enforcement to cover it up. The allegations led to an unprecedented impeachment hearing, something not attempted in 102 years.

"Robert Bentley, governor of Alabama, directed law enforcement to advance his personal interests over those of the state," Jack Sharman, special counsel for the House Judiciary Committee, told state lawmakers Monday afternoon. "In timelines characterized by increasingly desperate conduct, he subjected honest career law enforcement to tasks to protect his reputation, both political and personal."

It is the first ever impeachment directed at an Alabama governor, and the first impeachment the chamber had considered since 1915.

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Bentley's resignation cuts short those proceedings. Throughout this past week he had maintained his innocence, denied doing anything illegal and insisted he would not resign.

On Wednesday, the Alabama Ethics Commission found probable cause that the governor had violated ethics and campaign finance laws and forwarded its findings to Montgomery County's district attorney, Daryl Bailey, for further prosecution.. The report proved a major blow to Bentley and what little political capital he had remaining in the Legislature.

By early Friday afternoon, Senate President Pro Tem Del Marsh and House Speaker Mac McCutcheon — both Republicans who had previously steered clear of comments on impeachment or Bentley's legal woes — called on Bentley to resign.

Those calls came before the release of a damaging impeachment report Friday afternoon, which depicted Bentley as obsessed with recovering recordings of conversations between him and Mason that then-first lady Dianne Bentley had made. Bentley threatened staffers who knew or whom he thought knew about the affair and sent law enforcement to recover the tapes or question those he thought might know about them.

The governor also is accused of using a member of his security team on at least two occasions to try to break up with Mason.

The report alleges Bentley brought Mason with him in state vehicles and aircraft, at times overriding his security detail to do so. Sharman said he requested and received pre-edited flight logs.

The report also depicted the governor becoming emotionally unstable over the relationships, wavering between tearful contrition and angry defiance, to the point of threatening staffers who knew or who he believed knew about the existence of the tapes.

By Monday, Bailey had sent the state Ethics Commission findings to Ellen Brooks, serving as acting attorney general in a probe that office is conducting into Bentley's conduct. Alabama Attorney General Steve Marshall, appointed by the governor in February, recused himself from Bentley investigation shortly afterward.

The impeachment report was one of a host of struggles the governor faced. Two days prior, the Alabama Ethics Commission found probable cause that the governor violated ethics and campaign finance laws, and forwarded their findings to Montgomery County District Attorney Daryl Bailey for further prosecution. Bailey sent those findings Monday to Ellen Brooks, serving as acting attorney general in a probe that office is conducting into Bentley's conduct. Alabama Attorney General Steve Marshall, appointed by the governor in February, recused himself from the investigation shortly afterward.

Jack Sharman, the special counsel for the House Judiciary Committee, began his opening arguments Monday against Bentley, mainly outlining the history of impeachment and the Alabama Constitution's somewhat hazy description of it.

"Impeachment is the people’s check against political excess," Sharman told the committee. "It is a remedy of the state as opposed to punishment for an individual as in a criminal case."