Devout Catholic dad-of-six Dominic Perrottet is the likely successor to Gladys Berejiklian if she succumbs to romance scandal - but he pledges his loyalty to Premier of 'utmost integrity'

Gladys Berejiklian's deputy - a devout Catholic father-of-six - has pledged his loyalty to the New South Wales Premier after her secret relationship with a disgraced MP was revealed.

Treasurer Dominic Perrottet could, at 38, make history as the youngest-ever leader of Australia's biggest state should Ms Berejiklian resign and create a vacancy.

Hours after the Premier appeared before the Independent Commission Against Corruption, Mr Perrottet stood by her side - amid Liberal Party rumours he was the favourite to become the next premier.

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Gladys Berejiklian's deputy Dominic Perrottet - a devout Catholic father-of-six - has pledged his loyalty to his boss after the New South Wales Premier's secret relationship with a disgraced MP was revealed

'Can I say, it's great to be here with the Premier today to offer my support to her,' he said.

'It’s been a very difficult day but she is somebody with the utmost integrity, honesty.'

Mr Perrottet declared he had been a loyal deputy leader of the Liberal Party.

'As somebody who has stood by her side as the deputy leader and Treasurer of this state, never have I seen someone work so hard, a person of high integrity, honesty and somebody who puts the people of New South Wales first and foremost,' he said.

Three hours earlier, he had donned a fluoro yellow vest for an announcement about the development of Green Square in Sydney's inner south.

'Laying the groundwork for hundreds of jobs and transforming our city,' he posted on Facebook. 

Less than 8km away, Ms Berejiklian was appearing before the ICAC where she revealed she had been in a secret relationship since 2015 with disgraced former Liberal MP and property lobbyist Daryl Maguire, after taped phone calls between the couple were played at the inquiry.

Treasurer Dominic Perrottet would, at 38, make history as the youngest-ever leader of Australia's biggest state should Ms Berejiklian resign

The 50-year-old Premier, who is unmarried and has no children, admitted she 'stuffed up' by secretly dating Mr Maguire from 2015 to 2018 - but said she would not step down.

'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,' she said.

'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 was 'far from perfect' but insisted she has 'done nothing wrong' and has not been compromised by her relationship with 61-year-old father-of-two Mr Maguire, who recently divorced ex-wife Maureen.

Hours earlier, however, Mr Perrottet used the phrase 'laying the groundwork' in a Facebook announcement about the development of Green Square in Sydney's inner south

As he donned a fluoro yellow vest, Ms Berejiklian appeared before ICAC and revealed she had been in a secret relationship since 2015 with disgraced former Liberal MP Daryl Maguire after taped phone calls between them were played at the inquiry

Should he succeed Ms Berejiklian, Mr Perrottet would be the state's fifth premier in just a decade.

During the past 32 years, NSW has had three 40-year-old premiers: Nick Greiner in 1988, Nathan Rees in 2008 and Kristina Keneally in 2009.

Mr Perrottet, is believed to have the support of moderate faction convenor Matt Kean, who is understood to be positioning himself to be the Liberal Party's next deputy leader and treasurer.

In November 2018, Daily Mail Australia saw Mr Perrottet and Mr Kean at a Liberal Party fundraiser featuring right-wing former prime minister Tony Abbott at the Magpies club of Waitara on Sydney's Upper North Shore. 

Mr Perrottet, is believed to have the support of moderate faction convenor Matt Kean, who is understood to be positioning himself to be the Liberal Party's deputy leader and treasurer

A NSW Liberal Party source said Mr Perrottet was the favourite to be the next premier, with Mr Kean's support, despite a scandal with iCare, the state workers' compensation insurer

Mr Kean's appearance at a Right-faction event, despite being a leader of the moderate faction, was considered unusual but strategic within the Liberal Party.

A NSW Liberal Party source said Mr Perrottet was the favourite to be the next premier, with Mr Kean's support, despite a scandal with iCare, the state workers' compensation insurer.

'This is a matter of choosing the least worst candidate. Like Labor, we have too few options,' the source told Daily Mail Australia. 

Should he become the next premier, Mr Perrottet would break a long-standing tradition stretching back more than three decades where Liberal leaders have either come from the moderate side of the party or been social liberals.

Should he become the next premier, Mr Perrottet would break a long-standing tradition stretching back more than three decades where Liberal leaders have either come from the moderate side of the party or been social liberals

Nonetheless, Mr Perrottet is reaching out to the moderate side of the party, worried about his deeply conservative religious views.

'It has to be said Dom is a lot more moderate and diplomatic these days,' the Liberal Party source said.

His main leadership rival Attorney-General Mark Speakman, a former barrister, is shaping up as the key candidate of the moderate faction.