In a difficult interview for the Deputy Prime Minister on the ABC's 730 program, Mr Joyce said the end of his marriage was one of the "greatest failures" of his life, criticised the Daily Telegraph's decision to publish a photo of a pregnant Vikki Campion on its front page and insisted he had never used public funds to conduct the relationship.

And he railed against the "salami-slicing" of MPs' private lives, delivering a robust defence of his conduct and arguing Australia should not go down the same path as the United States, where politicians' private lives are public fodder.

Mr Joyce and his new partner were thrust into the public eye on Wednesday after it was revealed they are expecting a baby, sparking a fierce debate about media intrusion into politicians' personal lives.

As the extraordinary events unfolded, Mr Joyce's wife Natalie - from whom he is separated - spoke publicly about the devastating impact of her husband's actions on their family, including their four daughters.

The deputy PM sat stony-faced through question time, and answered an inquiry about regional infrastructure to rare silence from the chamber.

"I can't quite fathom why, basically, a pregnant lady walking across the road deserves a front page," he told the ABC on Wednesday evening.

"I don't think it helps anybody in the future to start making this a public discussion. As much as I can, I will keep private matters private."

Mr Joyce told host Leigh Sales that it was fair to ask about his use of public expenses, but added there was "no problem" and that numerous Freedom of Information requests by media organisations had examined the issue and found nothing untoward.

"They have inquired into this and nothing has been found because there's nothing there. We have made sure that private matters remain private and anything on the - on a public account has been to do with my work as a politician," he said.

Mr Joyce said the end of his marriage was "one of the greatest failures in my life" and added that anyone "who has been through a marriage break-up would understand that" and that it was "incredibly painful".

He dismissed "social media commentary", highlighted by Sales, that has suggested that his support of the definition of marriage as being between a man and a woman during last year's debate about legalising same-sex marriage, while his personal life was in turmoil, was hypocritical.

"Just because my relationship didn't work, it doesn't mean I changed what I think. On that instance I failed, OK. I'll be upfront I failed on that one, but I am not going to say therefore just because I failed I'm going to completely change my views and definition."

Similarly, Mr Joyce rejected suggestions of a power imbalance in the relationship between him and his former staffer in the workplace.

Turnbull government ministers and Nationals colleagues expressed sympathy for Mr Joyce, while others, including Labor frontbenchers, declined to comment on "a private matter".

Defence Industry Minister Christopher Pyne slammed the expose as "tabloid journalism" and told 5AA radio: "I think it's a great pity that this has happened to Barnaby Joyce and his family, and it must be very traumatising for everyone, made much worse by being publicised on the front page."

During the debate over same-sex marriage last year, Mr Joyce confirmed his own marriage of a little over two decades to Natalie had broken down. Many commentators pinned Mr Joyce as a hypocrite for his advocacy of traditional marriage and family values, although the deputy PM largely took a back seat during the postal vote campaign on marriage equality.

Earlier on Wednesday, in a statement to News Corp, Mrs Joyce said she was "deeply saddened by the news that my husband is now having a child with a former staff member". She said the affair "has been going on for many months and started when she was a paid employee".

“Our family life has had to be shared during Barnaby’s political career and it was with trust that we let campaign and office staff into our homes and into our lives," Mrs Joyce said. "Naturally we also feel hurt by the actions of Barnaby and the staff member involved."

Ms Campion was previously a media adviser to Mr Joyce and is a former Telegraph journalist. In recent months, rumours had circulated in Canberra about Mr Joyce's impending fatherhood, but until now they had been dismissed or denied by the parties involved.

Rumours also plagued Mr Joyce on the streets of his New England electorate during the byelection campaign he fought and won last year following his disqualification over dual citizenship.

Journalist Sharri Markson, who wrote the story, defended it as being in the public interest. Comparisons were also drawn to coverage of New Zealand prime minister leader Jacinda Ardern's pregnancy.

Small Business Minister Craig Laundy lamented, however, the "collateral damage" inflicted on Mr Joyce's family.

"My heart goes out to the wife and daughters," he told Sky News. "I think politicians personal lives should not be the subject of the scrutiny we've seen today."