Former Newt Gingrich backer and casino magnate Sheldon Adelson has followed through on his promise to support Mitt Romney after the Massachusetts governor secured the Republican nomination — and in a big way.

Adelson has given $10 million to Restore Our Future, the super-PAC supporting Romney's presidential election effort, according to a report in The Wall Street Journal. The $10 million gift is likely the largest single donation toward either candidate's super-PAC since the campaign began.

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While Restore Our Future is prohibited by federal election law from directly coordinating with the Romney campaign, many of the presumptive GOP nominee's former aides are involved in the administration of the group. During the Republican primaries, the organization spent around $45 million to help Romney's effort and reported in May that it had around $8 million in cash reserves heading into the general election.

Adelson was a fervent supporter of Gingrich's super-PAC during the Republican primary, pouring more than $20 million into his effort. But after Gingrich fell helplessly behind in the delegate count, the billionaire signaled that he would likely shift support to Romney's candidacy.

Late last month, Romney and Adelson privately conferred before a fundraiser in Las Vegas that also featured Gingrich and real estate mogul and reality television star Donald TrumpDonald John TrumpHouse Democrat slams Donald Trump Jr. for ‘serious case of amnesia’ after testimony Skier Lindsey Vonn: I don’t want to represent Trump at Olympics Poll: 4 in 10 Republicans think senior Trump advisers had improper dealings with Russia MORE. Adelson had previously pledged to spend some $100 million on conservative efforts during the 2012 election.

The donation is expected to pad the conservative advantage with super-PACs, which have been easily outpacing efforts on the left. 

Romney's campaign itself has seen an uptick in donations, besting the president in May. Romney's campaign raised $76.8 million for a joint committee between his campaign and the Republican National Committee, versus $60 million for President Obama and the Democratic National Committee.