Former New York mayor, billionaire entrepreneur and media magnate Michael Bloomberg contributed nearly $20 million to help boost President Biden in his 2024 election rematch with former President Trump, sources confirm to Fox News.

Bloomberg, a one-time Republican turned independent turned Democrat, wrote a massive $19 million check to the Future Forward PAC, known as the FF PAC, which is the leading super PAC supporting Biden's bid for a second term in the White House.

And Bloomberg, who briefly ran unsuccessfully against Biden for the 2020 Democratic presidential nomination, also gave the maximum donation of $929,600 to the Biden Victory Fund, a fundraising committee that benefits the president's re-election campaign and various Democratic Party committees.

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Bloomberg announces climate summit venue

Michael Blomberg speaks at a United Nations Climate Change Conference at The Plaza Hotel, on September 19, 2023 in New York City. (Bryan Bedder/Getty Images for Bloomberg Philanthropies)

Sources with knowledge of the transfers confirmed them to Fox News on Thursday evening.

"I stood with Joe Biden in 2020, and I am proud to do so again," Bloomberg said in a statement to the Washington Post, which was the first news organization to report the massive contributions.

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Bloomberg shelled out a staggering $1 billion of his own money on his 2020 Democratic presidential nomination bid.

After he dropped out of the race, he transferred roughly $18 million to the Democratic Party. And he separately announced the funding of a $100 million independent ad campaign to boost Biden's White House bid.

President Joe Biden speaks at podium in Philadelphia

President Biden speaks at a campaign rally in Philadelphia, Pennsylvania, on May 29, 2024. (Demetrius Freeman/The Washington Post via Getty Images)

Bloomberg, who at 82 is a year older than Biden, according to Forbes Magazine, is the 15th wealthiest person in the world, with approximately $106 billion in assets.

As the news of the Bloomberg contributions was going viral, so was word that conservative billionaire donor Timothy Mellon gave a mind-boggling $50 million contribution last month to a leading super PAC supporting Trump's White House bid.

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According to a federal disclosure filing on Thursday, Mellon made his contribution to Make America Great Again (MAGA) Inc. the day after Trump was convicted of all 34 felony counts in his criminal trial, which is the first involving a former or current president in the nation's history.

The New York Times was first to report the contribution from Mellon, who's an heir to the Pittsburgh-based Mellon banking family.

Former President Donald Trump, the presumptive GOP presidential nominee, walks to the podium at a campaign event Tuesday, June 18, 2024, in Racine, Wis. (AP Photo/Jeffrey Phelps)

Former President Donald Trump, the presumptive GOP presidential nominee, walks to the podium at a campaign event Tuesday, June 18, 2024, in Racine, Wis. (AP Photo/Jeffrey Phelps) (AP Photo/Jeffrey Phelps)

In its fundraising filings, MAGA Inc. disclosed that it brought in over $68 million in fundraising last month, with most of the money coming from Mellon, with another $10 million from the conservative mega donors Dick and Liz Uihlein, founders of the Uihlein shipping and packaging company.

The super PAC announced a few days after the Mellon donation that they were reserving $100 million in ad reservations to run spots this summer in support of Trump.

The latest contribution from Mellon follows a previous $25 million donation earlier this cycle to MAGA Inc. Mellon also contributed roughly the same amount to American Values, the main super PAC supporting Democrat turned independent Robert F. Kennedy Jr.'s presidential campaign.

The Bloomberg and Mellon news came as the Biden campaign announced that they and the Democratic National Committee raised a combined $85 million in May, which is their second-best month of fundraising this election cycle.

But the money raised by Biden and the DNC is far short of the staggering haul raised bytTrump's campaign and the Republican National Committee last month.

In announcing their May fundraising figures on Thursday evening, the Biden campaign also highlighted that they had a massive $212 million cash-on-hand as of the end of May. 

"Our strong and consistent fundraising program grew by millions of people in May, a clear sign of strong and growing enthusiasm for the President and Vice President every single month," Biden campaign manager Julie Chavez Rodriguez said in a statement. 

Biden's announcement came on the final day the presidential campaigns had to file their May fundraising figures with the Federal Election Commission (FEC).

But the Trump campaign didn't wait for the deadline to tout its May fundraising haul.

The former president's campaign announced two and a half weeks ago that they and the RNC, fueled in part by the former president's guilty verdicts in his criminal trial, combined hauled in a stunning $141 million in fundraising in May.

That was up from the $76 million they raised in April when they topped President Biden and the DNC for the first time in their 2024 election rematch. 

Fundraising, along with public opinion polling, is a key metric used to measure the strength of a candidate and their campaign. Money raised can be used to build up grassroots outreach and get-out-the-vote operations, staffing, travel and ads, among other things.

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.