Jane Sanders is writing a book about 'her and Bernie's experience together in public service,' the Democratic presidential candidate's campaign says.

Sanders has already received an advance on the book of at least $106,250 from St. Martin's Press, a subsidiary of Macmillan. The advance is reflected in the couples' 2017 tax documents.

A campaign aide told DailyMail.com that the date of publication has not been decided on. The campaign disclosed the existence of the memoir when it released ten years of the Sanders' tax returns.

Jane Sanders is writing a book about 'her and Bernie's experience together in public service,' the Democratic presidential candidate's campaign says

The Sanders' tax documents show that they earned well over $1 million on the book Bernie Sanders wrote about his long-shot bid for the White House. Sanders' 2016 memoir was an instant best-seller.

He told DailyMail.com on Saturday that he would not 'apologize' for writing the best-selling book that has been translated into at least five languages and declined on Monday at a televised town hall to explain why he gave just 3.4 percent of his wealth away to the poor.

In addition to the salary he makes as a U.S. senator, he earns royalties off his books. Jane's only individual source of income appears to be the memoir she's writing — she has primarily served as an unpaid adviser to her husband's political organizations for the last several years, having parted ways with Burlington College in 2011 over allegations that she misspent the non-profit's money.

Jane and Bernie Sanders' campaign books are published by St. Martin's Press. The company did not immediately respond to a request for comment on Tuesday on the manuscript that his wife is said be penning.

Sanders' campaign disclosed Jane's book in a statement on the couple's tax returns on Monday. It released ten years worth of the documents, fulfilling a promise that the candidate made and then dragged his feet on weeks prior.

Jane Sanders is listed as a 'writer' on the couples' 2018 IRS form suggesting that she spent much of the last writing the as-of-yet unpublished book that St. Martin's Press paid her more than $100,000 up front to write.

She recently announced that she and her son David Driscoll were ending their work at a think tank named after her husband. They'd come under scrutiny for the $100,000 annual salary he received for work, in light of Bernie Sanders' latest White House bid.

The Sanders Institute, as it is called, will close its doors in May. It will not reopen until the end of his next campaign for higher office.

Bernie and Jane Sanders donated $25,000 to the organization in 2017. They made charitable contributions to other organizations equivalent to their gross adjusted income in 2018 of 3.4 percent, the senator's presidential campaign disclosed.

Bernie Sanders told DailyMail.com on Saturday that he would not 'apologize' for writing the best-selling book that has been translated into at least five languages and declined on Monday at a televised town hall to explain why he gave just 3.4 percent of his wealth away to the poor

That amount does not include proceeds from his book 'The Speech,' his campaign stated, because they are donated directly to charity.

'The Sanders’ donations have gone primarily to senior centers, low-income organizations, educational entities, and environmental and housing advocacy groups,' the campaign claimed.

His campaign acknowledged in the same statement on the Sanders' tax returns that Jane has a book coming out.

'In 2016, the Sanders’ income increased substantially due to advances and royalties from his best-selling book Our Revolution: A Future To Believe In, which has been translated into 5 languages and published in a number of countries,' the statement said.

'The youth version of Our Revolution, the publication of Where We Go From Here and an advance on a book currently being written by Jane Sanders, are also reflected in the tax filings.'

In the couples' 2017 tax documents, Jane Sanders is revealed to have made $106, 250 off her work as a book author.

The advance is handsome but not nearly as sizable as the $14 million that Hillary Clinton received for 'Hard Choices' or the eye-popping $65 million that Barack and Michelle Obama received for their post-White House memoirs.

Sanders' husband's best-selling book, 'Our Revolution,' received $795,000 advance. He received an advance of $63,750 on a children's adaptation of the book.

The Vermont senator admitted last week that the campaign tome he published after he failed to win the Democratic nomination in 2016 yielded more than a million-dollar profit.

Asked by DailyMail.com on Saturday at a campaign stop in Gary, Indiana, if his millionaire status 'conflicts' with the message he's pushing, Sanders, who's seeking the presidency again, replied, 'I don't think so.

'I didn't know it was a crime to write a good book,' he said to applause from participants of a breakfast roundtable his campaign had put together.

Bernie Sanders, accompanied by the Gary, Indiana, police chief, walks into a roundtable

Sanders is on a bus tour of the upper Midwest. His first stop on Saturday was Gary. He addressed question from DailyMail.com about his wealth, having written a best-selling book

Sanders claimed he did not want to take Americans' wealth, he wants them to pay a higher rate of taxes on it.

'My view has always been that we need a progressive tax system which demands that the wealthiest people in this country finally start paying their fair share of taxes,' he said.

'If I make a lot of money, you make a lot of money, that is what I believe,' he told his guests. 'So, I don't apologize for writing a book that was number three on the New York Times Best Seller, translated into five or six languages.'

Sanders published a campaign manifesto days after Hillary Clinton lost the presidency to Donald Trump. It opened at No. 3 on the New York Times Best Sellers list

He successfully changed the subject after he told traveling and local press he was bothered by the inquiry.

'Maybe we might want to talk about Gary, Indiana. Maybe we might want to talk about poverty,' he said 'This might be a great moment to talk abut something else we should discuss.'

The democratic socialist's central campaign message over two presidential runs has been an assault the millionaires and billionaires of the country and a demand that they pay their 'fair share' in taxes to fund universal healthcare, tuition-free college and a litany of other progressive promises.

Sanders has said that billionaire President Donald Trump should release his tax returns, even though the longtime legislator had not put out his own until Monday.

He said in an interview last week that his book 'Our Revolution: A Future to Believe In' raked in more than a million dollars in profit.

'I wrote a best-selling book,' he told the New York Times. 'If you write a best-selling book, you can be a millionaire, too.'

Sanders released a second book, 'Where We Go from Here: Two Years in the Resistance,' in November.