It was the bombshell no-one saw coming.

Gladys Berejiklian's admission of a "close personal relationship" with the former member for Wagga Wagga, Daryl Maguire, has exposed a huge vulnerability for the deeply private Premier.

The contradiction between Ms Berejiklian as the steadfast, by-the-book, risk-averse leader and a relationship that was at the very least misjudged after multiple allegations against Mr Maguire, is as surprising as it is unfathomable.

After Mr Maguire resigned from Parliament in 2018, disgraced by an admission to a separate ICAC inquiry that he sought payment from brokering a deal with a Chinese property developer, Ms Berejiklian said she was "deeply disappointed" by the revelations.

In the by-election that followed, the Liberals lost the Wagga Wagga seat they had held for 50 years to independent Joe McGirr, after a 29 per cent swings against the Liberals.

At the time, Ms Berejiklian said the local electorate had sent a strong message.

"I regret that the people of the Wagga region came to the conclusion that they could no longer trust the way in which they were being represented.

And yet she still persisted in the relationship, which continued, she told the inquiry today, until "a few months ago".

The relationship, which began in 2015, and is now under spotlight as ICAC investigates whether Mr Maguire used his position for personal gain, has become the biggest threat to Ms Berejiklian's political career.

The question is simply over her judgment in putting herself in that position — whereas politically, she's never been a stronger force.

Over the past 12 months, Ms Berejiklian has racked up a mostly impeccable record in the firm steering of the state through unprecedented crises.

There were the bushfires that ravaged 5.5 million hectares over a long and weary summer.

Then the pandemic, where she displayed the same level of fortitude, navigating the state through the coronavirus outbreak, in a performance only significantly marred by the Ruby Princess debacle, for which she "unreservedly" apologised.

Now all of this is tainted.

It is not about whether Ms Berejiklian is permitted to have a relationship with another political figure, or anyone at all.

But a relationship with a man at the centre of corruption investigations is a different story.

Today's revelation weakens her internally — with her enemies within the right always looking to pounce, this could be their moment.

This is no suggestion of any wrongdoing on Ms Berejiklian's part.

She told the inquiry today she never turned a blind eye to any wrongdoing — but the problem is the perception, is it possible to plead ignorance about the conduct of somebody you are in a close relationship with?

What could save Ms Berejiklian is public support — or whether they'll care enough about this revelation.

The bombshell reveals a human side to Ms Berejiklian, one of a personal and fallible nature, which might even soften her image.

But among Macquarie Street players there has never been a whisper about any of Ms Berejiklian's relationships — and today's confession would have blindsided all sides.

Without question this will be a tough week: Daryl Maguire is up before the inquiry this week. Parliament is also sitting, so there's no option for her other than to front her colleagues.

This chink in her armour revealed today severely weakens the previously squeaky clean, untouchable politician.

Now Saint Gladys, the unrelentingly devoted public servant, has shown that she can be a mere mortal who, like the rest of us, can on occasion be struck by poor judgement, particularly when it comes to personal relationships.