NSW Premier Gladys Berejiklian has declared: "I won't resign" over bombshell revelations that she conducted a clandestine relationship with a former MP who is now the subject of a corruption probe.

After confessing for the first time that she was in a "close, personal relationship" with the father of two, Ms Berejiklian has declared she has no intention of standing down as premier.

"I'm an intensely private person and without question, I stuffed up in my personal life," Gladys said in a press conference on Monday afternoon.

"It's very difficult for someone in my position to have a private and personal life, and I'm very upset at what has transpired. But I want to make this assurance to the people of New South Wales - I have always put the public first. I have always made sure the public interest is first and foremost paramount in every single thing that I do.

"The integrity of the role I have - the office that I hold - is the greatest privilege of my life. And whilst I have made this mistake in my personal life, I intend to serve the people of New South Wales to the best of my ability. That's what I've always done. I've sacrificed my life to

public office, and I'm proud of that."

Ms Berejiklian said she had trusted someone who had let her down in the worst way.

"I want to state at the outset that, had I known then what I know now, clearly I would not have made those personal decisions that I did," she said.

"I trusted someone that I'd known for a long time, and I feel really, really let down. I trusted him for a long time. We were colleagues for 15 years. And I'm not going to take away from the fact that I made a mistake in my personal life, but I have to say that there is huge separation between a personal life and public office.

"And I can't stress enough that, every day that I've been in this job, I have held myself accountable to the highest standards."

There is no suggestion of wrongdoing by Ms Berejiklian according to the Independent Commission Against Corruption, but her colleagues are seriously questioning her judgment today over the revelations of a secret relationship.

She refers to the disgraced former MP in phone calls as her "numero uno."

Ms Berejiklian told the inquiry the secret relationship began after the 2015 election and she had not ceased contact with him until she appeared at a private ICAC hearing in August. Their last conversation was on September 13.

Earlier, Ms Berejiklian said she was "shocked and disturbed" by the evidence to ICAC about the activities of her former boyfriend.

"I can't tell you what I felt. Beyond shocked. Shocked, disgusted, let down. All of the above."

But during one intercepted phone call played at the ICAC hearing Ms Berejiklian told Mr Maguire: "I don't need to know about that bit" when the pair discussed a lucrative business deal during a private phone call.

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MP Daryl Maguire and NSW Premier Gladys Berejiklian in Wagga in 2017. Picture: Supplied
MP Daryl Maguire and NSW Premier Gladys Berejiklian in Wagga in 2017. Picture: Supplied

Ms Berejiklian was repeatedly asked today if she was telling him to keep her in the dark because she didn't want to know what he was doing because it might have consequences for her public duties.

In evidence to the Independent Commission Against Corruption, Ms Berejiklian tried to downplay the exchange insisting she may have been "bored" and wasn't telling him to limit the information he told her.

"Perhaps I was bored and busy and wanted to move on,'' she said.

The day before the pair had discussed Mr Maguire's financial difficulties and his hopes that the deal would help him pay off his debts.

For a woman who has cultivated an image as a goody two shoes, NSW Premier Gladys Berejiklian's big reveal she was in a secret relationship with Mr Maguire has rendered most of her colleagues simply speechless.

There is now speculation that Attorney-General, Mark Speakman, and Treasurer, Dominic Perrottet are emerging as top contenders for the role of NSW Premier if Ms Berejiklian resigns.

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Gladys Berejiklian with Daryl Maguire and Barry O'Farrell. Picture: Twitter
Gladys Berejiklian with Daryl Maguire and Barry O'Farrell. Picture: Twitter

Senior sources within the party told The Australian she cannot continue in her role as Premier, after revealed she was in a close personal relationship with former Wagga Wagga Liberal MP Daryl Maguire - the man at the centre of a corruption inquiry.

"You can't be f***ing a guy involved in (alleged) high-level government corruption and survive it. She's gone for all money," one source said.

As private phone calls between the pair were played to her in the witness box today, she flinched as Mr Maguire let the f-bombs fly during the discussion that was secretly intercepted by the corruption watchdog.

Mr Maguire can be heard delivering a lengthy monologue complaining "they're all sucking people's dicks" and "they can get f**ked".

But her ex-boyfriend's bad language is the least of her problems today given the dramatic revelations at the ICAC hearing.

Even harder to swallow is the revelation that she continued that "close, personal relationship" after she demanded he resign from Parliament in disgrace two years ago.

In July 2018, the New South Wales Premier urged Mr Maguire to reconsider his position in politics after secret phone recordings of him discussing potential developer "dividends" were played at another Sydney corruption inquiry.

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NSW Premier Gladys Berejiklian departs after giving evidence at the NSW Independent Commission Against Corruption. Picture: Sam Mooy/Getty Images
NSW Premier Gladys Berejiklian departs after giving evidence at the NSW Independent Commission Against Corruption. Picture: Sam Mooy/Getty Images

Ms Berejiklian said she felt "deep disappointment" after learning of the recordings, but didn't bother to tell voters or colleagues she was in a "close, personal relationship" with him at the time.

"Whilst it is for Mr Maguire alone to determine whether he stays on as the elected member until next March, I would encourage him to think carefully as to whether he can effectively represent the people of Wagga Wagga from here on in," Berejiklian said in a statement at the time.

Those comments are now seen in an entirely different light given she was conducting a secret relationship with him at the time.

At the time, Mr Maguire had quit the Liberal party two days earlier, after the ICAC inquiry heard telephone conversations of him trying to arrange a "dividend" for helping arrange a multi-million property sale to a Chinese developer.

But instead of resigning effective immediately, Mr Maguire announced he would stay on but retire at the next election.

"I do apologise - I did breach a very strict code of conduct and I have to suffer the consequences but I won't put the taxpayer to the cost of having a by-election - I think that unreasonable and I think it's a cost the taxpayer doesn't need,'' he said.

He ultimately resigned from Parliament in August, 2018. But according to Ms Berejiklian's own evidence she continued her relationship with Mr Maguire until recently when she knew there was a full-blown ICAC inquiry into his activities.

The NSW Independent Commission Against Corruption (ICAC) is investigating allegations that, from 2012 to August 2018, Mr Maguire engaged in conduct that involved a breach of public trust by using his public office, involving his duties as a member of the NSW Parliament, and the use of parliamentary resources, to improperly gain a benefit for himself and/or entities close to him. These entities included G8wayinternational/G8wayinternational Pty Ltd and associated persons.

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Gladys Berejiklian and Daryl Maguire. Picture: Newswire; AAP
Gladys Berejiklian and Daryl Maguire. Picture: Newswire; AAP

The NSW Premier has told the inquiry that she "did not care" about Mr Maguire's financial position and had "never relied on anybody else in my life".

"If you're suggesting that I cared about his financial position, I reject that completely. I did not care. That was his business, it had nothing to with me,'' she said.

"I've never relied on anybody else in my life. And I wouldn't start then."

However, she conceded that Mr Maguire was "obsessed" with his financial position and that they discussed it in relation to his exit from politics.

"Absolutely, he was obsessed with it. Yeah,'' she said.

Looking back, Ms Berejiklian said she did not believe Mr Maguire had been entirely truthful with her over his financial position.

"Looking back, I'm not sure whether he was truthful about that, if I can be frank. I don't know if anything that… said to me was truthful,'' she said.

Her explanation for not telling colleagues she was in a secret relationship with Mr Maguire included that she was "a very private person" and didn't feel the relationship had "sufficient substance" to be made public.

"We were close," she said.

But the wisdom of continuing that "close, personal, relationship" with Mr Maguire after he resigned in disgrace because he was in "a bad state" is now very likely to trigger her own exit from politics.

Mr Maguire will front ICAC later this week and is expected to give evidence for three days.

Originally published as 'I stuffed up': Gladys speaks out