Missouri Governor Eric Greitens has denied allegations that he slapped his former mistress during an encounter in the same hospital just as his wife was giving birth to their child.

The former mistress, who claimed that Greitens attempted to blackmail her with an explicit photo at the start of their affair, has also accused the Republican governor of assault, CBS News reported on Friday.

Prosecutors have launched an investigation into the claims made by a married woman with whom Greitens had an affair.

The affair was revealed by the mistress' now-ex-husband.

St. Louis Circuit Attorney Kimberly M. Gardner confirmed the probe in a statement Thursday after the 'serious' and 'troubling' allegations were made public through an audio tape released by the unnamed woman's ex-husband this week.

Missouri Governor Eric Greitens (shown with wife Sheena Greitens in 2016) is denying allegations that he assaulted a former mistress while his wife was in the hospital giving birth to their child

St. Louis Circuit Attorney Kim Gardner (pictured left) announced her probe into Greitens after the Republican politician's married ex-mistress says he blackmailed her at the start of their affair. Greitens admitted to an affair, but denied blackmail claims

Greitens is pictured with his family during a campaign event in August 6, 2016. He admitted to having a sexual relationship with the unnamed woman in March 2015

'It is essential for residents of the City of St. Louis and our state to have confidence from leaders. They must know that the Office of the Circuit Attorney will hold public officials accountable in the same manner as any other resident of our city,' Gardner said in the statement.

'Both parties and the people of St. Louis deserve a thorough investigation of these allegations.

'If anyone has any information related to this matter, I encourage them to contact my office immediately.'

The married father-of-two, 43, admitted Wednesday to sleeping with the married woman, but denied her claim suggesting that he tied her up, blindfolded her and snapped photos to later use as blackmail if she failed to keep quiet.

The ex-husband's attorney, Albert Watkins, made another explosive allegation on Friday, accusing the governor of slapping his client after she told him she and her husband had sex during their attempt at reconciliation.

'When she admitted that she'd had sexual relations with her husband during a period of reconciliation, that the governor slapped her,' Watkins said.

The attorney alleged on Friday that the governor first assaulted his client when they met face-to-face in a hospital where Greitens' wife was delivering their child.

The governor is denying the allegations.

The sexual relationship between the woman and the Republican politician, who assumed office in January 2017, began in March 2015, his former lover's now ex-husband revealed in the bombshell story to St. Louis TV station KMOV.

In the audio recording, the woman purported to be Gretiten's lover is heard telling her husband about a physical interaction she had with the lawmaker just days earlier.

The woman said she met Greitens, a client, at her hair salon roughly one year before - when she revealed she was 'instantly' attracted to him.

In an audio recording which hears the conversation between the unidentified woman and her then-husband, she explains intimate details of the sexual affair

The distraught woman can be heard weeping in the audio as he explains the disturbing parts of the encounter that went from fun to frightening

The woman's ex-husband who spoke on the matter, still refuses to forgive Greitens for his 'inhuman' and 'evil' behavior

One Saturday morning in March of the following year, she went to his house, where the two had sex for the first time.

Then he allegedly threatened to expose naked images of her if she told anyone what happened.

The distraught woman can be heard weeping in the audio tape as she explains the disturbing parts of the encounter that went from fun to frightening.

'He used some sort of tape, I don't know what it was... and taped my hands to these rings and then put a blindfold on me,' she first explained.

Then, 'he stepped back, I saw a flash through the blindfold and he said: 'You're never going to mention my name, otherwise, there will be pictures of me everywhere',' she added, tearfully.

In the 2015 conversation with her husband, the woman said she partly blames herself for the said interactions.

She felt angry, however, when Greitens - a man who described himself during his campaign as a 'Navy SEAL, native Missourian and most importantly, a proud husband and father' - snapped a nude picture of her without permission to later use as blackmail.

The woman also said Greitens since apologized over the aggressive encounter, and confirmed: 'I wanted to tell you, I erased it.'

Following the fallout, the woman revealed the two had one more physical encounter later in the day - but did not include further information on what that entailed.

The lawmaker is pictured wearing festive sweaters with his family in December 5, 2017. He has denied allegations from his former mistress who says he threatened her with a compromising photo

The family man is shown during his campaign in July 26, 2016. Greitens attorney says the woman's claim is false

KMOV reported that in October 2015, the woman used the same gmail account formerly used to secretly talk to Greitens, and asked him to no longer see her at work.

The email read: 'Eric, I am asking you to please consider all who are involved and the circumstances around us. I need you to not book at the salon anymore.

'This isn't fair to me, nor anyone close to us. Please respect me and my wishes. I need to move forward in my life as I know you are doing as well. Take care.'

Her ex-husband said although she attempted to reconcile, he was ready to move forward. The couple sought divorce in March 2016.

Meanwhile, Greitens' wife stood by his side, over what the lawmaker calls a 'deeply personal mistake' of his past.

The woman's ex-husband, who spoke openly on the matter with the news station, added: 'I don't want to be a part of politics, I don't want to be a part of anything.'

Greitens emerges as winner of the Missouri governor's race on Nov. 8, 2016. Following his affair, his wife Sheena (right) chose to stick by his side

He also continues to refuse forgiveness for Greitens over his 'inhuman' and 'evil' behavior.

'He took a picture of my wife naked as blackmail... there is no worse person,' the man told the news station.

'I think it's as bad as it gets when somebody takes advantage of somebody.'

He revealed he only opened up about it after being contacted by law enforcement and media members - who left a voicemail on his daughter's cell phone.

While the politician has come forward to admit to the affair, his attorney, James F. Bennett, has denied the blackmail claims.

'There was no blackmail, and that claim is false,' Bennett said in a public statement. 'This personal matter has been addressed by the Governor and Mrs. Greitens privately years ago when it happened.

'The outrageous claims of improper conduct regarding these almost three-year-ago events are false.'