Democratic presidential contender Bernie Sanders announced he will release 10 years of his tax returns and revealed he is a millionaire thanks to his best-selling book 'Our Revolution.'

'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 said he would release his returns by Tax Day on Monday and said he hoped President Donald Trump would do the same.

'On the day in the very immediate future, certainly before April 15, we release ours, I hope that Donald Trump will do exactly the same. We are going to release 10 years of our tax returns, and we hope that on that day Donald Trump will do the same,' he told The Times.

Bernie Sanders announced he will release 10 years of his tax returns and revealed he is a millionaire

Sanders said he made his money thanks to his book 'Our Revolution'

Sanders did not release his tax returns when he ran for president in 2016, which did not garner much attention at the time.

But with Trump under heavy Democratic fire for not releasing his, the Independent senator from Vermont is making his tax documents public.

Sanders, however, brushed aside any comparisons to the president.

'Not being a billionaire, not having investments in Saudi Arabia, wherever he has investments, all over the world, mine will be a little bit more boring,' he said.

Sanders told CBS News there no 'great revelations' in his returns.

'I make what a United States senator makes. I wrote two books in recent years. One of those books was a bestseller on the New York Times bestseller list translated into five or six languages. It did very well. I made money on that book,' he said.

His Democratic competition - Sens. Amy Klobuchar and Kirsten Gillibrand and Gov. Jay Inslee - have released this year's returns. Sen. Elizabeth Warren has also released 10 years worth of tax documents.

Sanders said he and his wife fill out their own tax forms and don't use an accountant.