Billionaire Timothy Mellon, a major supporter of U.S. President Donald Trump, has been identified as the anonymous donor behind a $130-million contribution to help fund troop salaries during the ongoing government shutdown.

Trump called the mysterious benefactor a “patriot” and a “great American citizen” but declined to reveal his name. Mellon — heir to the famed banking dynasty and one of Trump’s biggest political backers — has previously poured hundreds of millions into conservative causes.

While the White House and the Pentagon confirmed the donation was accepted under “gift authority,” experts warn it may test the Antideficiency Act, which bars federal spending beyond congressional appropriations.